how to evaluate variables within character string in C

Question

Sorry for asking a basic question but how would I do the following to get the pid to be part of the file name like this:

int pid;
int fOUT;enter code here
pid=getpid();
// TRYING TO EVALUATE HERE
char* filename=printf("hello-world-%i.txt", pid); # obviously wrong 
//char* filename="here.txt";
fOUT= open (filename, O_RDWR | O_CREAT | O_SYNC);

thx for any help

Use [`sprintf`](http://en.cppreference.com/w/cpp/io/c/fprintf), or preferably: `snprintf`. — Kninnug, Nov 25 '13 at 20:23

score 3 · Accepted Answer · edited May 23 '17 at 10:25

3

You can use snprintf and allocated buffer for this:

#include <limits.h>

// ...

char filename[PATH_MAX];
snprintf(filename, sizeof(filename), "hello-world-%d.txt", pid);

About PATH-MAX: Where is PATH_MAX defined in Linux? and this link.

edited May 23 '17 at 10:25

Community

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answered Nov 25 '13 at 20:23

Nemanja Boric

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@timpone See the edit - it should be the `maximum number of bytes in a pathname, including the terminating null character.` Also, see this link, if it is important for you: http://www.gnu.org/software/hurd/hurd/porting/guidelines.html. – Nemanja Boric Nov 25 '13 at 20:29
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great, thx for answer. works like a charm; need to wait a few – timpone Nov 25 '13 at 20:32
@timpone - _what should MAX_PATH be?_ typically defined as 260. Always safer to use macro rather than hard-coding a value though. – ryyker Nov 25 '13 at 20:45

score 2 · Answer 2 · answered Nov 25 '13 at 20:22

2

You are looking for snprintf, or perhaps more conveniently (but less portably) asprintf.

answered Nov 25 '13 at 20:22

zwol

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how to evaluate variables within character string in C

2 Answers2