在退出時關閉檔案描述符是一個很好的做法

檔案自動關閉,但這是一個很好的做法.

在這個例子上見valgrind

david@debian:~$cat demo.c
#include <stdio.h>

int main(void)
{
FILE *f;

f = fopen("demo.c", "r");
return 0;
}
david@debian:~$valgrind ./demo
==3959== Memcheck, a memory error detector
==3959== Copyright (C) 2002-2010, and GNU GPL'd, by Julian Seward et al.
==3959== Using Valgrind-3.6.0.SVN-Debian and LibVEX; rerun with -h for copyright info
==3959== Command: ./demo
==3959== 
==3959== 
==3959== HEAP SUMMARY:
==3959==in use at exit: 568 bytes in 1 blocks
==3959==total heap usage: 1 allocs, 0 frees, 568 bytes allocated
==3959== 
==3959== LEAK SUMMARY:
==3959==definitely lost: 0 bytes in 0 blocks
==3959==indirectly lost: 0 bytes in 0 blocks
==3959==possibly lost: 0 bytes in 0 blocks
==3959==still reachable: 568 bytes in 1 blocks
==3959==suppressed: 0 bytes in 0 blocks
==3959== Rerun with --leak-check=full to see details of leaked memory
==3959== 
==3959== For counts of detected and suppressed errors, rerun with: -v
==3959== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 4 from 4)

如你所見,它會引起記憶體洩漏

在某些情況下,您可以使用atexit()：

#include <stdio.h>
#include <stdlib.h>

static FILE *f;

static void free_all(void)
{
fclose(f);
}

static int check(void)
{
return 0;
}

int main(void)
{
atexit(free_all);
f = fopen("demo.c", "r");
if (!check()) exit(EXIT_FAILURE);
/* more code */
return 0;
}