question
stringlengths 24
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stringlengths 5
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|
|---|---|
When I doing my assigment , I am string to use this formatscanf("%[^\n]%*c",s);in putty but it said
```
writing into constant object (argument 2) [-Wformat=]
scanf("%[^\n]%*c",s);
```
I want to input string with white space:
```
const s[10000];
```
| Changeconst char s[10000]-->char s[10000]
Code cannot write to aconstarray. It is not a format issue forscanf().
|
```
int num = 65537;
char p = (char)num; //char = 1;
```
Whats going on here?
Is itp=num%(127+128)-1orp=num%256or something else?
I need to know why p is equal to 1.
thanks!
| since 65537 is00000000 00000001 00000000 00000001in binary, but the char type has only 1 byte, the last byte is considered for the char value, wich is00000001 = 1
|
```
function(void * p)
```
pis an address containing an address to a struct. I cannot get from the given address to the address within to display the data that it points to. There is a really simple solution to do this, however I do not know how to dereference from the given address, and use the information I get as a new address.
| Just cast to the type you're looking for.
```
MyStruct **pps = (MyStruct**)p;
(**pps).Member = ...
```
|
```
function(void * p)
```
pis an address containing an address to a struct. I cannot get from the given address to the address within to display the data that it points to. There is a really simple solution to do this, however I do not know how to dereference from the given address, and use the information I get as a new address.
| Just cast to the type you're looking for.
```
MyStruct **pps = (MyStruct**)p;
(**pps).Member = ...
```
|
Specifically, I'm storing URLs and ports and storing them in a table. A pair would be ("www.beej.us", 80) or ("8.8.8.8", 22). Does it make sense to append the integer onto the string and hash on the final string?
Thanks for the help!
| For better performance and minimizing collisions, you would better write a hash function as follows:
```
hash(host) * prime_greater_than_65536 + port
```
|
This question already has answers here:String literals: Where do they go?(8 answers)Closed8 years ago.
For example this code here:
```
char *s = "Hello";
```
Where is "Hello" being stored? Is it stored the same in memory just anonymously?
| String literals have static storage duration and are allocated in the static memory that is neither on the stack nor in the heap. For example they can be allocated in a read only data segment.
|
This question already has answers here:String literals: Where do they go?(8 answers)Closed8 years ago.
For example this code here:
```
char *s = "Hello";
```
Where is "Hello" being stored? Is it stored the same in memory just anonymously?
| String literals have static storage duration and are allocated in the static memory that is neither on the stack nor in the heap. For example they can be allocated in a read only data segment.
|
Q:Could someone give a hint, why inside my program here are conflicting types, even if its the same?
| If you call a function before it is defined (i.e. earlier in the file than the definition), the compiler won't know the argument types and return type. You need to have a function prototype before the function is called. Usually people put function prototypes in header files, but you could just add one near the top of your file.
|
Q:Could someone give a hint, why inside my program here are conflicting types, even if its the same?
| If you call a function before it is defined (i.e. earlier in the file than the definition), the compiler won't know the argument types and return type. You need to have a function prototype before the function is called. Usually people put function prototypes in header files, but you could just add one near the top of your file.
|
Hi I program in c and I like using clion. Is there a way to change how the default files it creates in a new project? I would like it to create a main.c and the make file to reflect that.
| ReadHow to create a C project with CLion. It's not possible to create a C project by default, but you could use the info of that post to prepare CMakeLists.txt.
|
I have a server program running.
I want to connect 1000 clients to it and observe how the server is working. I also want to save the output to a file for analyzing.
My server is just an echo server.
| You can use netcat:
```
for ii in {1..1000}; do
(echo "testing"; sleep 5; echo "goodbye") | nc localhost 12345 > out.$ii &
done
wait # for all to finish
```
|
In Linux I can do this by checking the /proc/pid/status file and looking for a line: Threads: 1 (or any number). How can I achieve the same in FreeBSD? I am not interested in any interactive tool. Is there any C function, or a system file? I have tried BSD's procfs and and linprocfs and I could not find any similair feature there.
| You want:
procstat -t <pid>
This answer is short, but I'm typing more to get the answer up to the minimum length.
|
Is the memory lost until a reboot or does VS have some safe-mechanism to handle that? I've always wondered...
| The leaked memory will be freed when the process leaking the memory is closed and the operating system cleans up.
|
I have achar *p = "abcd", how can I access the elements'a','b','c','d'using only C(not C++)? Any help would be appreciated .
| You can use indexing:
```
char a = p[0];
char b = p[1];
/* and so on */
```
Equivalently you can use pointer arithmetic, but I find it less readable:
```
char a = *p;
char b = *(p+1);
```
If you really want to surprise someone you can also write this:
```
char a = 0[p];
char b = 1[p];
/* and so on */
```
|
```
typedef struct A
{
int* whatever;
} A;
int main(void)
{
A* foo = (A)malloc(sizeof(A));
foo->whatever = (int)malloc(sizeof(int));
free(A); // leak? (foo->whatever)
return 0;
}
```
Do I have to free each component of a struct / composite data type, or can I just free the struct?
| Anything that is malloc'd needs to be freed
|
I want to test my c code for big endian on Windows (On x86-64). How can we do this?
| Assuming that you don't have any actual big-endian hardware to hand, your best bet is to use a virtual machine such asQEMUto emulate a big-endian architecture such asSPARCorPowerPC.
You'll then need to install a suitable operating system on your VM - perhapsDebianwould suit your needs.
|
I want to test my c code for big endian on Windows (On x86-64). How can we do this?
| Assuming that you don't have any actual big-endian hardware to hand, your best bet is to use a virtual machine such asQEMUto emulate a big-endian architecture such asSPARCorPowerPC.
You'll then need to install a suitable operating system on your VM - perhapsDebianwould suit your needs.
|
```
int i=0;
int array[1000]={0};
srandom(23523);
a0=random();
a1=random();
a2=random();
....
a999=random(); //a0,a1,...a999 are some random numbers
for(i=0;i<999;i++){
....
//array[0]=a0 array[1]=a1 array[2]=a2....array[999]=a999
}
```
My goal is to change the values in array to a0, a1...a999.
How to do it by using for loop in C?
| If you already know the values you don't need a loop.
```
int array[3]= { 0, 14, 22 };
```
|
Using C in a Windows in a Kernel Mode Driver using KMDF, how do I determine the owner a of file?
I searched high and low but could not find any hint. Only C++ and of course Csharp.
| After opening a handle to a file, you can use the kernel-modeZwQuerySecurityObjectto get the owner information (and full DACL).
|
I'm learning on how to use signals in C with POSIX threads.
I know how to signal threads from main, but how to signal my main from the thread to notify it that it has finished some job? I need the PID of my main. How should I go about doing it?
How can I let my threads know mains PID to send a signal to it?
| In the main threadgetpid() == gettid(), so, you can usegetpid()orgettid()to get PID of main thread.
|
I'm learning on how to use signals in C with POSIX threads.
I know how to signal threads from main, but how to signal my main from the thread to notify it that it has finished some job? I need the PID of my main. How should I go about doing it?
How can I let my threads know mains PID to send a signal to it?
| In the main threadgetpid() == gettid(), so, you can usegetpid()orgettid()to get PID of main thread.
|
Is there anyway to open an sqlite database in c without having to have the sqlite exes and dlls.
Is there a lib to do this.
I only want to read the database, not write.
| Have you taken a look at theSQLite3 C/C++ interface?
(See the second bulletpoint of the section titled "Write Programs that use SQLite" at the bottom ofthis pagefor a quick example on how to use it.)
|
I want to know how to get all data from a gtk treeview (row and column) and put it in a logfile, I know how to create the log, my problem is getting all data, I already know how to get the selected row, but not all rows at once.
| gtk_tree_model_foreach is your friend.
|
If I have this code block
```
char *array[] = {"element1" , "eLement2"};
char *p ;
char *pc;
```
How can I point*pto the first String"element 1"andhow can I point*pcto the second character of the second StringLand then print those two using printf
| p = array[0]
pc = array[1]+1
This should do the trick
|
If I have this code block
```
char *array[] = {"element1" , "eLement2"};
char *p ;
char *pc;
```
How can I point*pto the first String"element 1"andhow can I point*pcto the second character of the second StringLand then print those two using printf
| p = array[0]
pc = array[1]+1
This should do the trick
|
If I have this code block
```
char *array[] = {"element1" , "eLement2"};
char *p ;
char *pc;
```
How can I point*pto the first String"element 1"andhow can I point*pcto the second character of the second StringLand then print those two using printf
| p = array[0]
pc = array[1]+1
This should do the trick
|
I want to pack the lowest two bytes of an integer into another in integer, an stuck at this
```
for ( int i = 0; i < 8 ; i ++){
if ((bitmask & ( 1 << i)))
result |= 1 >> i;
}
```
| Endian-independent solution:
```
x = ((y >> 0) & 0xFF) |
((y >> 8) & 0xFF);
```
|
I am using a macro defined in the same source file as:
```
#define MY_MACRO (a, b,...) (...)
```
The macro is being used later in the file.
However, the compiler complains:
error: a undeclared (first use in this function).
It's really weird.. am I missing something obvious?
| I think the problem is that there is a SPACE betweenMY_MACROand(a, b, ...). It should be like this:
```
#define MY_MACRO(a, b,...) (...)
```
|
I am writing some C code with Eclipse + CDT + MinGW.
The compilation output always shows:
```
Info: Internal Builder is used for build
gcc -O0 -g3 -Wall -c -fmessage-length=0 -o Math.o "..\\Math.c"
```
How can I change the command line parameters such as -O0, -Wall?
(I am new to Eclipse IDE.)
| For GCC, the setting is in project properties => C/C++ Build => Settings => GCC C Compiler => Optimization.
|
I am writing some C code with Eclipse + CDT + MinGW.
The compilation output always shows:
```
Info: Internal Builder is used for build
gcc -O0 -g3 -Wall -c -fmessage-length=0 -o Math.o "..\\Math.c"
```
How can I change the command line parameters such as -O0, -Wall?
(I am new to Eclipse IDE.)
| For GCC, the setting is in project properties => C/C++ Build => Settings => GCC C Compiler => Optimization.
|
Suppose I want to generate a very long, repetitive string, such as
```
"foo bar bar bar bar ... bar"
```
wherebaroccurs 1,000 times in the final result. What would be the easiest way to do this without having memory leaks?
| The first thing that came to my mind is:
```
char *string = malloc(4004);
int i;
strcpy(string, "foo");
for(i = 0; i < 1000; i++)
strcat(string, " bar");
```
|
I need to initialize a typedef struct pointer
in header file,
```
typedef struct {
DWORD RxBuf[4];
DWORD Tr0c;
} t, *p_t;
```
In the cpp file,
```
static p_t p1
= {
{0x00,0x00,0x00,0x00},
0
};
```
| Just a guess, I believe you want to do:
```
static t tNull
= {
{0x00,0x00,0x00,0x00},
0
};
static p_t p1 = &tNull;
```
|
I need to initialize a typedef struct pointer
in header file,
```
typedef struct {
DWORD RxBuf[4];
DWORD Tr0c;
} t, *p_t;
```
In the cpp file,
```
static p_t p1
= {
{0x00,0x00,0x00,0x00},
0
};
```
| Just a guess, I believe you want to do:
```
static t tNull
= {
{0x00,0x00,0x00,0x00},
0
};
static p_t p1 = &tNull;
```
|
Now, when I print each element in my block array, each one has the same address. For example:
```
ints: 20 bytes stored at 0xbffa84fc
doubles: 80 bytes stored at 0xbffa84fc
chars: 8 bytes stored at 0xbffa84fc
Students: 1008 bytes stored at 0xbffa84fc
```
| ```
blk->addr = &blk;
```
The address of the allocated memory actually isblkitself. But here, you are using&blk, i.e, the address ofblk.
|
So far, I can print in one column quite nicely :
```
for (i = 0 ; i < *lengthOfFile ; i++)
{
fprintf(myFile, "%d\n", thisArray[i]);
}
```
Easy enough. However, how would I go about printing in columns of ten if say I have 20 or 100 or 10000 or more numbers?
Anything would help very much, thank you!
| You can print "%d\t" instead of "%d\n", and move the "\n" into its own print statement that only occurs when (i % 10) == 0.
|
If I have an array declared as
```
char arr[1] = "";
```
What is actually stored in memory? What will a[0] be?
| Strings are null-terminated. An empty string contains one element, the null-terminator itself, i.e,'\0'.
```
char arr[1] = "";
```
is equivalent to:
```
char arr[1] = {'\0'};
```
You can imagine how it's stored in the memory from this.
|
If I have an array declared as
```
char arr[1] = "";
```
What is actually stored in memory? What will a[0] be?
| Strings are null-terminated. An empty string contains one element, the null-terminator itself, i.e,'\0'.
```
char arr[1] = "";
```
is equivalent to:
```
char arr[1] = {'\0'};
```
You can imagine how it's stored in the memory from this.
|
Why does this hang without first printing?
```
#include <stdio.h>
void main() {
printf("hello world");
while (1) {}
}
```
| Because you haven't flushed the standard output. Tryfflush. Even better, for C++ use...
```
std::cout << "hello world" << std::endl;
```
Separately, you'd have a better chance of it flushing itself if you added a\n, but not all implementations follow the Standard when it comes to such things.
|
Why does this hang without first printing?
```
#include <stdio.h>
void main() {
printf("hello world");
while (1) {}
}
```
| Because you haven't flushed the standard output. Tryfflush. Even better, for C++ use...
```
std::cout << "hello world" << std::endl;
```
Separately, you'd have a better chance of it flushing itself if you added a\n, but not all implementations follow the Standard when it comes to such things.
|
Why does this hang without first printing?
```
#include <stdio.h>
void main() {
printf("hello world");
while (1) {}
}
```
| Because you haven't flushed the standard output. Tryfflush. Even better, for C++ use...
```
std::cout << "hello world" << std::endl;
```
Separately, you'd have a better chance of it flushing itself if you added a\n, but not all implementations follow the Standard when it comes to such things.
|
I'v been use some module manager like npm for node.js or apt-get in ubuntu, I find it's really easy to build more. And I just want to know is there a cpm for module manage in c programming?
| clibmay be the answer.https://github.com/clibs/clibit is proposed to offer some stand-alone "micro c libraries".
|
Is there an option that I can use to separate parts of my GUI with lines in Glade 3? I want some widgets to be separated from the others; for example I would like to put them in a box.
| Use GtkSeparator; its icon is the vertical line in the Control and Display section of the tool palette.
|
I developed a program in which I use a http client with libcurl.
I want to find out the source tcp port used by libcurl in a tcp session.
How can I do that ?
| curl_easy_getinfowith theCURLINFO_LOCALPORToption!
|
Glibc provides the very handybacktrace()andbacktrace_symbols()functions, which can help getting the stack trace of the current function programmatically (see here).
Does the Windows API provide any similar functions?
| Yes, take a look at the functionCaptureStackBackTrace(). UseSymFromAddr()and its counterparts to get meaningful symbol names.
|
Given an API like this :
write_data(uint32_t address,uint8_t *data)
how can I transmit a constant to my embedded device, like 0x001 ?
| You create a variable and assign the constant to it. Then you pass a pointer to the variable.
|
This question already has answers here:What does void mean in C, C++, and C#?(15 answers)Closed8 years ago.
What is the value that is stored in void()? Basically it is used before a function which doesnot return anything. But does simply void holds any value?
| Void is an incomplete type which, by definition, can't be an lvalue.
That means it can't get assigned a value.
So it also can't hold any value.
|
This is my program :
```
#include<stdio.h>
int main()
{
int *n;
int var;
scanf("%d",n);
printf("%d",*n);
}
```
asscanfstores the value at specified address I am giving the address .Then I am trying to print value at address but its giving segfault.
| You should allocate memory for pointers like this:
```
int* n = (int*)malloc(sizeof(int))
```
|
I am working on a project in which If I could include a header file at runtime, it would save some programming effort. I google'd about it, but all in vain. My question is :Can we include header files in a C program at runtime ?If yes, how?If not, why?
| In C the source files are only read compile-time, so the answer to your question isnot. Runtime there is only the executable binary, which has nothing to do with your source code headers.
|
i have created macro as following
```
#define log printf("(%s):(%d) ",__FUNCTION__, __LINE__);printf
```
And i am using it in main function for logging
```
log("Hello world\n");
```
it is resulting in run time error as "lldb".
Error in IDE is displaying "called object type 'int' is not a function or function pointer in x code"
| Try:
```
#define LOG( s ) printf( "(%s):(%d)%s\n", __FUNCTION__, __LINE__, s );
```
|
I see many programmers that include "utils.h" to their program.
Tried to search for what it is exactly and what is the proper use of utils.h, but all I found was different versions of the file.
So what is it exactly?
| Many programmers define common functionalities inutils.cand declare them inutils.h. You could implement for example command line parsing methods in utils.h / utils.c.
But utils.h is no standard file to be included.
|
I see many programmers that include "utils.h" to their program.
Tried to search for what it is exactly and what is the proper use of utils.h, but all I found was different versions of the file.
So what is it exactly?
| Many programmers define common functionalities inutils.cand declare them inutils.h. You could implement for example command line parsing methods in utils.h / utils.c.
But utils.h is no standard file to be included.
|
How do I write nothing inifpart if the condition is true?
For example:
```
if(true)
// I want to keep this space blank or want compiler to do nothing here
else
break;
```
How do I do this?
| Typically, this is written by negating the condition:
```
if (not true)
break;
```
|
How can I write three different matrices of different sizes say A, B and C using C?
The doubt being that once a particular row is printed the cursor is in the bottom most position, now how do we bring it back up?
| You don't. you plan in advanced the rows and then print each row (one you go down - you can't go up....)
If you can't handle the logic - use a 2d array to store everything and then print it.
|
How do I write nothing inifpart if the condition is true?
For example:
```
if(true)
// I want to keep this space blank or want compiler to do nothing here
else
break;
```
How do I do this?
| Typically, this is written by negating the condition:
```
if (not true)
break;
```
|
How can I write three different matrices of different sizes say A, B and C using C?
The doubt being that once a particular row is printed the cursor is in the bottom most position, now how do we bring it back up?
| You don't. you plan in advanced the rows and then print each row (one you go down - you can't go up....)
If you can't handle the logic - use a 2d array to store everything and then print it.
|
What is the unary-& doing here?
```
int * a = 1990;
int result = &5[a];
```
If you were to printresultyou would get the value 2010.
You have to compile it with-fpermissiveor it will stop due to errors.
| In C, x [y] and y [x] are identical. So &5[a] is the same as &a[5].
|
Is it possible to intercept primitive operations (+,-,% etc.) like this one, with LD_PRELOAD?
```
int64_t endWhenNsec = startWhenNsec + gTimeLimitSec;
```
If not, any way to achieve something similar?
| No. Primitive operators are compiled directly to machine code. There is no library involved, so preloading libraries cannot alter their behavior. What a mess if it could!
|
Is there any way to do this withstrtokfunction? or any suggestions ?
Example :
```
Insert "hello world" to dbms
```
Result:
```
Insert
"hello world"
to
dbms
```
| strtokor any other function in the standard C library can't do this for you. To get it, you have to write code for it yourself, or you have to find some existing code in some external library.
|
According to the man page for pause, it returns -1 and sets errno to EINTR.
Why does it do this? I understood -1 to mean a failure, not something operating as normal.
| The only timepause()stops pausing is when it is interrupted, and that is a return on failure (to continue pausing). So, correctly, it returns -1 to indicate that it failed to continue pausing.
|
Is it possible to clear the output at the command prompt using C on windows?
For example, on linux I could do
```
printf("\033[2J");
```
But as far as I know windows doesn't recognise the ANSI escape codes
Thanks.
EDIT: I guess I'll also need to get the cursor back to 0,0 fo r the next output after the clear...
| There are many way to do that on windows.
You includeconio.hand call_clrscr();
Or you can callsystem("cls");
|
I have the following function in assembly, but I need it in C. The code is:
```
push ebp
mov ebp, esp
mov eax, DWORD PTR [ebp+8]
add eax, 1667940388
pop ebp
ret
```
Could anybody translate this into C for me. Thanks.
| Sorry for the silly mistake on theeaxreturn value ... its' fixed now ... my assembly is a little rusty :)
```
int function(int value)
{
return value + 1667940388;
}
```
|
I have the following function in assembly, but I need it in C. The code is:
```
push ebp
mov ebp, esp
mov eax, DWORD PTR [ebp+8]
add eax, 1667940388
pop ebp
ret
```
Could anybody translate this into C for me. Thanks.
| Sorry for the silly mistake on theeaxreturn value ... its' fixed now ... my assembly is a little rusty :)
```
int function(int value)
{
return value + 1667940388;
}
```
|
I have the following function in assembly, but I need it in C. The code is:
```
push ebp
mov ebp, esp
mov eax, DWORD PTR [ebp+8]
add eax, 1667940388
pop ebp
ret
```
Could anybody translate this into C for me. Thanks.
| Sorry for the silly mistake on theeaxreturn value ... its' fixed now ... my assembly is a little rusty :)
```
int function(int value)
{
return value + 1667940388;
}
```
|
How do I create a soft link programmatically in C/C++? link() system call in freebsd will create a hard link.
| The system call you want issymlink(2).
```
#include <unistd.h>
int symlink(const char *name1, const char *name2);
```
A symbolic linkname2is created toname1
|
What could be the simplest way to split strings in an array and put it to array of array of strings in C.
For example
```
["this is a test", "this is also a test"]
```
into
```
[["this", "is", "a", "test"], ["this", "is", "also", "a", "test"]]
```
| Usestrtokfunction from the C library. The function splits a string into a serie of tokens.
http://man7.org/linux/man-pages/man3/strtok.3.html
|
How can I set the socket buffer size for a UNIX socket file descriptor in C?
I understand setsockopt is probably the system call involved...
Can anyone give an example of how to use it, the one's I have found do not explain how to set the buffer size?
| On Ubuntu 14.04 Linux check outman 7 socket, and specifically look atSO_RCVBUFandSO_SNDBUF.
|
Is there a way using the OpenLDAP API to set a particular network interface address to be used for socket bind on the LDAP client on a multi homed machine; like you do with the LDAP_OPT_SOCKET_BIND_ADDRESSES option with Microsoft's LDAP client.
| You can do it by creating and binding and connecting the socket yourself and then calling ldap_init_fd() to turn it into an LDAP connection.
|
I'm developing in c, using visual studio 2013.
I wonder if there is a way in visual studio, or a plugin, that enable to refactor names of variable/functions ...
If not, Is there any other recommended IDE that enables refactoring with C?
Thanks.
| Visual Assist(commercial) andVisual C++ Refactoring(free) extensions for VS 2013 support the rename refactoring for C.
|
How to generate random numbers with rand() and srand() without time.h in C ?
| You could try givin another seed to the random generator like the program's pid.
```
srand(getpid());
int num = rand();
```
|
```
for (int i = 0; i< n; i++)
arr[arr[i]%k] += k;
```
I'm new to programming and I came across this piece of codehere. Can anyone explain what it does?
| Translate to:
```
for (int i = 0; i< n; i++) {
int temp1 = arr[i];
int temp2 = temp1%k;
int temp3 = arr[temp2];
arr[temp2] = temp3+k;
}
```
Edit: thanks for the correction @R Sahu
|
Does K&R 2nd edition explain the usage of typedefs to make declaration and use of function pointers easier? I lost my copy and can't recollect of it does or it does not.
Thanks.
| Yes, this is explained in section 6.7, "Typedefs".
|
How can I tell what version of the C library python's zlib module was built with?
Specifically, I want to tell whether it was a new enough version to support ZLIB_RSYNC=1
This is different than the version of the zlib pythonmodule, but instead the version of the underlying C library
| It iszlib.ZLIB_VERSION:
```
>>> import zlib
>>> zlib.ZLIB_VERSION
'1.2.7'
```
|
How can I tell what version of the C library python's zlib module was built with?
Specifically, I want to tell whether it was a new enough version to support ZLIB_RSYNC=1
This is different than the version of the zlib pythonmodule, but instead the version of the underlying C library
| It iszlib.ZLIB_VERSION:
```
>>> import zlib
>>> zlib.ZLIB_VERSION
'1.2.7'
```
|
From which file ifconfig command takes input for displaying ip address, inet addr and h/w addr ?. I want this information for my presentation. Any file apart from /etc/network/interfaces is there ? Looking foreword for help.
| It's in the manual man. just run commandman ifconfigin your terminal and at bottom it says
it comes from these three files:
```
FILES
/proc/net/socket
/proc/net/dev
/proc/net/if_inet6
```
Hope it works.
|
If the following array contained shell code in a C program on a LINUX machine
```
char buf [100]
```
then how does the following execute this shell code :
```
((void(*)())buf)()
```
| Simple. It castsbufto a pointer-to-function taking no arguments and returningvoid, and then invokes that function.
However, that probably won't work since the page containingbufis highly unlikely to be marked as executable.
|
I am reading the current directory and printing it out using
```
printf("%s\n", file->d_name);
```
but it also prints out "." and ".." files. How can I exclude them?
| The simple way: just make sure the file name isn't"."or".."before you display it. :P
```
if (strcmp(file->d_name, ".") && strcmp(file->d_name, "..")) {
printf("%s\n", file->d_name);
}
```
|
I'm trying to create a game for my CS assignment and I'm stuck with this for loop that won't end my game even though the lives are already at zero.
```
for(life = 3, ai_life = 3; ai_life != 0, life != 0; --ai_life, --life)
```
| Please read up what thecomma operatordoes
```
for(life = 3, ai_life = 3; ai_life != 0 && life != 0; --ai_life, --life)
```
|
Lets say I am in /home/myuser
there are 90,000 files there inside 3000 directories.
How can I write a bash function or with linux commands to get one random file?
It could be C as well I suppose
| You can list all your files and then pick a random line between them:
```
find /home/myuser | sort -R | head -n1
```
However this is not very efficient, and could take a while, but is easy to understand. You can work from here.
|
I am reading the current directory and printing it out using
```
printf("%s\n", file->d_name);
```
but it also prints out "." and ".." files. How can I exclude them?
| The simple way: just make sure the file name isn't"."or".."before you display it. :P
```
if (strcmp(file->d_name, ".") && strcmp(file->d_name, "..")) {
printf("%s\n", file->d_name);
}
```
|
I'm trying to create a game for my CS assignment and I'm stuck with this for loop that won't end my game even though the lives are already at zero.
```
for(life = 3, ai_life = 3; ai_life != 0, life != 0; --ai_life, --life)
```
| Please read up what thecomma operatordoes
```
for(life = 3, ai_life = 3; ai_life != 0 && life != 0; --ai_life, --life)
```
|
```
int gcd(int x, int y) {
int t;
while (y) {
t = x;
x = y;
y = t % y;
}
return x;
}
```
Does it stop when y = 0? I thought the loop stops when y isn't defined.
| Yes, it stops when y is 0, what you have
```
while (y)
```
is short hand for
```
while (y != 0)
```
|
```
int foo(int n)
{
int sum = 0;
for(int k=1; k <= n; k = k * 2)
{
sum += k;
}
return sum;
}
```
I have the following function.
Now, according to me the runtime complexity of foo(n) should be big-o(logn).
Now, I am asked to find out the run time complexity of foo(n*n*n*n). What should it be?
According to me, it should be, big-o(logn) only.
Am I right in saying this?
| It is O(log n4) → O(4 log n) → O(log n)
|
```
int foo(int n)
{
int sum = 0;
for(int k=1; k <= n; k = k * 2)
{
sum += k;
}
return sum;
}
```
I have the following function.
Now, according to me the runtime complexity of foo(n) should be big-o(logn).
Now, I am asked to find out the run time complexity of foo(n*n*n*n). What should it be?
According to me, it should be, big-o(logn) only.
Am I right in saying this?
| It is O(log n4) → O(4 log n) → O(log n)
|
```
int main()
{
int a,i;
char b;
for(i=0;i<3;i++)
scanf("%c %d",&a,&b);
```
}
The program only scans twice (each for char and int) and then terminates.
OUTPUT
r
3
4
t
Now program is terminating rather than scanning two more times(one char and one int)
| ```
scanf(" %c %d",&a,&b);
```
solves the problem
|
```
int main()
{
int a,i;
char b;
for(i=0;i<3;i++)
scanf("%c %d",&a,&b);
```
}
The program only scans twice (each for char and int) and then terminates.
OUTPUT
r
3
4
t
Now program is terminating rather than scanning two more times(one char and one int)
| ```
scanf(" %c %d",&a,&b);
```
solves the problem
|
please could you help me understand what's __format in printf prototype for?
extern int printf (const char *__restrict __format, ...);
How can I find set of these in documentation?
Thanks!
| as per the ISO/IEC 9899:1999 declaration,
int printf(const char * restrict format, ... );
using the__is a variable nomenclature.
|
This question already has answers here:!! c operator, is a two NOT?(4 answers)Closed9 years ago.
While going over infrastructure code, I found this:
```
return !!(fin.flags & FIN_ACCEPT);
```
Does this has a meaning other than two logical nots in succession?
| !is logical negation.!!is logical negation applied twice.
It is typically used to normalise a boolean expression value to be either0or1.
|
```
struct tree{
#ifdef A
#define TREE_GET(x,y) &x->y
#else
#define TREE_GET(x,y) x->y
#endif
};
```
I want to know whether macro A was defined . Is there any command I can use in gdb .
| In compilation time we pass the -gdwarf-2 and -g3 flags to ensure the compiler includes information about preprocessor macros in the debugging information.
For example,g++ -gdwarf-2 -g3 program.cpp -o program
C Preprocessor Macros
|
```
struct tree{
#ifdef A
#define TREE_GET(x,y) &x->y
#else
#define TREE_GET(x,y) x->y
#endif
};
```
I want to know whether macro A was defined . Is there any command I can use in gdb .
| In compilation time we pass the -gdwarf-2 and -g3 flags to ensure the compiler includes information about preprocessor macros in the debugging information.
For example,g++ -gdwarf-2 -g3 program.cpp -o program
C Preprocessor Macros
|
```
int main()
{
static int fun(){}
return 0;
}
```
** If we define a function into another then why this code is giving following error:**
Error: invalid storage class for function ‘fun’
| This is called "nested function". It's not supported in C. Some compilers, such asgcc, offer it as language extension. You do not need thestatickeyword though.
|
What happens if you callopendir(argv[i])andargv[i]is the name of atextfile, not adirectory?
| Fromman opendir:
Return ValueTheopendir()andfdopendir()functions return a pointer to the directory stream. On error,NULLis returned, anderrnois set appropriately.
In this case,errnowould beENOTDIR: name is not a directory.
|
I initialized my array like this:char x[]={'m'};
It worked.
But for the following lines i got error:Size of the type is unknown or zero
```
char x[][]={{'m'},{'m'}};
```
or
```
char x[][]={{'m'}};
```
I am unable to find the reason of the error.
| While defining a 2D array, specifying the column size is mandatory.
```
char x[][1]={{'m'}};
```
|
I initialized my array like this:char x[]={'m'};
It worked.
But for the following lines i got error:Size of the type is unknown or zero
```
char x[][]={{'m'},{'m'}};
```
or
```
char x[][]={{'m'}};
```
I am unable to find the reason of the error.
| While defining a 2D array, specifying the column size is mandatory.
```
char x[][1]={{'m'}};
```
|
I would like to initialize an array of strings with \0.
Is it right to do it like this?
```
char first[1024][1024] = {'\0'};
```
| For a 2d array is better to use:
```
char first[1024][1024] = {{'\0'},{'\0'}};
```
or better yet (as suggested by @haccks):
```
char first[1024][1024] = {{'\0'}};
```
in order to avoid warnings.
|
i need to put many symbols in one array of char.
This is my code, I have problem with the single quote symbol, "'" :
```
int main()
{
int i, j;
int a;
char alph[] = {'A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z','0','1','2','3','4','5','6','7','8','9','.',',',':','?','=','-','(',')','"',''','/','%','@','!'};
}
```
| You can escape the quote with a backslash, i.e.'\''
|
I have a simple program like :
```
#include <stdio.h>
int main(void){
*(int*) 1 = 1;
return 0;
}
```
but why it is giving me Segmentation fault?
| This will most likely crash no most systems. The assignment
```
*(int*)1 = 1;
```
tries to assign 1 to the location in memory with address 1. This is very undefined behaviour, and in most of systems the memory protection mechanism raises an error when you try it.
|
I want to remove or hide some components from my window (button, combobox, etc). How can I do that?
| So, I've found answer on pelles-c forum:http://forum.pellesc.de/index.php?topic=6382.0
```
ShowWindow(hWnd, SW_HIDE);
// where hWnd - is some component
```
|
I have a simple program like :
```
#include <stdio.h>
int main(void){
*(int*) 1 = 1;
return 0;
}
```
but why it is giving me Segmentation fault?
| This will most likely crash no most systems. The assignment
```
*(int*)1 = 1;
```
tries to assign 1 to the location in memory with address 1. This is very undefined behaviour, and in most of systems the memory protection mechanism raises an error when you try it.
|
I want to remove or hide some components from my window (button, combobox, etc). How can I do that?
| So, I've found answer on pelles-c forum:http://forum.pellesc.de/index.php?topic=6382.0
```
ShowWindow(hWnd, SW_HIDE);
// where hWnd - is some component
```
|
This question already has answers here:Command-line Parameters in C program?(5 answers)Closed9 years ago.
How can I send parameters to main in C(Linux):
first one is -c or -d
second is a string like file.
How I'm doing that?
| First, send data to your program using command line argument Like @haccks said
Second, get the arguments in your code using :
```
int main(int argc, char **argv)
```
Tutorial Here
|
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