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Full Discussion: question about popen in C
Top Forums Programming question about popen in C Post 302505139 by Corona688 on Wednesday 16th of March 2011 10:43:28 AM
Old 03-16-2011
Maybe there's more than 512 bytes of output, and you're forcing it to close before it's finished? This will break the pipe, causing it to get the signal SIGPIPE which will kill it prematurely, which will give you a weird exit code.

You can also use the fread command since you've converted it to a FILE * anyway.

Code:
fread(buf, 1, 512, fp);

 

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FREAD(3)						     Linux Programmer's Manual							  FREAD(3)

NAME
fread, fwrite - binary stream input/output SYNOPSIS
#include <stdio.h> size_t fread(void *ptr, size_t size, size_t nmemb, FILE *stream); size_t fwrite(const void *ptr, size_t size, size_t nmemb, FILE *stream); DESCRIPTION
The function fread() reads nmemb elements of data, each size bytes long, from the stream pointed to by stream, storing them at the location given by ptr. The function fwrite() writes nmemb elements of data, each size bytes long, to the stream pointed to by stream, obtaining them from the location given by ptr. For nonlocking counterparts, see unlocked_stdio(3). RETURN VALUE
On success, fread() and fwrite() return the number of items read or written. This number equals the number of bytes transferred only when size is 1. If an error occurs, or the end of the file is reached, the return value is a short item count (or zero). fread() does not distinguish between end-of-file and error, and callers must use feof(3) and ferror(3) to determine which occurred. CONFORMING TO
C89, POSIX.1-2001. SEE ALSO
read(2), write(2), feof(3), ferror(3), unlocked_stdio(3) COLOPHON
This page is part of release 3.53 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/. GNU
2012-03-30 FREAD(3)
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