我有一个文件＆＃34; a＆＃34;，有2000个字符，char＆＃34; a＆＃34;只有，没有空格。
然后我有这个代码，它通过循环运行，将它添加到缓冲区，如果达到限制则最终重新分配，并且在错误时释放strBuffer变量。
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
int main()
{
int maxS = 200;
int numericExpression;
int strLength;
char *strBuffer;
strBuffer = malloc(sizeof(char)*maxS+1);
if(strBuffer == NULL)
{
printf("Failed to allocate requested memory!\n");
free(strBuffer);
strLength = sizeof(strBuffer);
printf("Freed %d bytes of memory!\n", strLength);
exit(99);
}
else
{
numericExpression = sizeof(char)*maxS+1;
printf("Alocated: %d Bytes of memory.\n", numericExpression);
}
// while simulation
int fcv = -1;
int numEx;
// file opening simulation
FILE* fd = fopen("a", "r");
int c;
while((c=fgetc(fd) != EOF)) // condition to make sure we realloc only once
{
fcv++;
strBuffer[fcv] = c;
if(fcv == (maxS))
{
printf("Additional memory space required!\n");
int strlensize = strlen(strBuffer);
numEx = (sizeof(char)*(2*strlensize));
strBuffer = realloc(strBuffer, numEx);
if(strBuffer == NULL)
{
printf("Failed to allocate requested memory!\n");
strLength = sizeof(strBuffer);
free(strBuffer);
printf("Freed %d bytes of memory!\n", strLength);
exit(99);
}
else
{
maxS = numEx;
printf("Reallocation successful!\n");
printf("Alocated: %d Bytes of memory.\n", numEx);
}
}
}
strLength = sizeof(strBuffer);
free(strBuffer);
printf("Freed %d bytes of memory!\n", strLength);
}
问题是它最终告诉我，我只释放了8个字节的内存。我想这是因为sizeof（strBuffer）没有响应预期的大小。当我使用strlen（strBuffer）时，我只释放2001个字节。
我想这可能只是打印掉释放的字节数的问题。我可能做错了。所以也许我只是无法分辨出我有多少字节。但后来我尝试了valgrind它告诉我，我不够自由，有内存泄漏。但是在程序的每个分支中，我都可以释放strBuffer使用的内存。
当我通过valgrind（＆＃34; valgrind ./realloc"）运行它时，它告诉我：
==780== Memcheck, a memory error detector
==780== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
==780== Using Valgrind-3.10.0.SVN and LibVEX; rerun with -h for copyright info
==780== Command: ./realloc
==780==
Alocated: 201 Bytes of memory.
Additional memory space required!
==780== Invalid read of size 1
==780== at 0x4C2E0F4: strlen (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==780== by 0x400846: main (in /home/dan/Desktop/test_ifj/realloc)
==780== Address 0x51fd109 is 0 bytes after a block of size 201 alloc'd
==780== at 0x4C2AB80: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==780== by 0x40078C: main (in /home/dan/Desktop/test_ifj/realloc)
==780==
Reallocation successful!
Alocated: 402 Bytes of memory.
==780== Invalid write of size 1
==780== at 0x400823: main (in /home/dan/Desktop/test_ifj/realloc)
==780== Address 0x51fd562 is 0 bytes after a block of size 402 alloc'd
==780== at 0x4C2CE8E: realloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==780== by 0x400866: main (in /home/dan/Desktop/test_ifj/realloc)
==780==
Additional memory space required!
Reallocation successful!
Alocated: 806 Bytes of memory.
Additional memory space required!
==780== Conditional jump or move depends on uninitialised value(s)
==780== at 0x4C2E0F8: strlen (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==780== by 0x400846: main (in /home/dan/Desktop/test_ifj/realloc)
==780==
Reallocation successful!
Alocated: 804 Bytes of memory.
Freed 8 bytes of memory!
==780==
==780== HEAP SUMMARY:
==780== in use at exit: 568 bytes in 1 blocks
==780== total heap usage: 5 allocs, 4 frees, 2,781 bytes allocated
==780==
==780== LEAK SUMMARY:
==780== definitely lost: 0 bytes in 0 blocks
==780== indirectly lost: 0 bytes in 0 blocks
==780== possibly lost: 0 bytes in 0 blocks
==780== still reachable: 568 bytes in 1 blocks
==780== suppressed: 0 bytes in 0 blocks
==780== Rerun with --leak-check=full to see details of leaked memory
==780==
==780== For counts of detected and suppressed errors, rerun with: -v
==780== Use --track-origins=yes to see where uninitialised values come from
==780== ERROR SUMMARY: 1200 errors from 3 contexts (suppressed: 0 from 0)
如何正确释放我分配的内存？所以它不会导致内存泄漏？最终 - 我做错了，有更好的方法吗？ 谢谢你的帮助。
我遵循建议并在1个上下文中得到3个错误。这就是我的代码现在的样子：
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
int main()
{
int maxS = 200;
int numericExpression;
char *strBuffer;
strBuffer = malloc((maxS+1));
if(strBuffer == NULL)
{
printf("Failed to allocate requested memory!\n");
printf("Freed %d bytes of memory!\n", maxS);
exit(99);
}
else
{
numericExpression = sizeof(char)*maxS+1;
printf("Alocated: %d Bytes of memory.\n", numericExpression);
}
// while simulation
int fcv = -1;
int numEx;
// file opening simulation
FILE* fd = fopen("a", "r");
if(fd == NULL)
{
printf("Error opening a file!\n");
if(strBuffer != NULL)
{free(strBuffer);}
exit(99);
}
int c;
char *tmpBuffer;
while((c=fgetc(fd)) != EOF) // condition to make sure we realloc only once
{
fcv++;
strBuffer[fcv] = c;
if(fcv == (maxS))
{
printf("Additional memory space required!\n");
numEx = ((2*fcv));
tmpBuffer = realloc(strBuffer, numEx);
if(!tmpBuffer)
{
free(strBuffer);
printf("Realloc() failed!\n");
exit(99);
}
else
{
strBuffer = tmpBuffer;
}
if(strBuffer == NULL)
{
printf("Failed to allocate requested memory!\n");
printf("Freed %d bytes of memory!\n", maxS); // well this is questionable, I think
exit(99);
}
else
{
maxS = numEx;
printf("Reallocation successful!\n");
printf("Alocated: %d Bytes of memory.\n", maxS);
}
}
}
free(strBuffer);fclose(fd); // ADDED, still errors occur
printf("Freed %d bytes of memory!\n", maxS);
}
使用相同的valgrind调用（＆＃34; valgrind ./realloc"）我得到了这个：
==1213== Invalid write of size 1
==1213== at 0x4007FD: main (in /home/dan/Desktop/test_ifj/realloc)
==1213== Address 0x51fd560 is 0 bytes after a block of size 400 alloc'd
==1213== at 0x4C2CE8E: realloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==1213== by 0x400831: main (in /home/dan/Desktop/test_ifj/realloc)
==1213==
Additional memory space required!
Reallocation successful!
Alocated: 800 Bytes of memory.
Additional memory space required!
Reallocation successful!
Alocated: 1600 Bytes of memory.
Additional memory space required!
Reallocation successful!
Alocated: 3200 Bytes of memory.
Freed 3200 bytes of memory!
==1213==
==1213== HEAP SUMMARY:
==1213== in use at exit: 568 bytes in 1 blocks
==1213== total heap usage: 6 allocs, 5 frees, 6,769 bytes allocated
==1213==
==1213== LEAK SUMMARY:
==1213== definitely lost: 0 bytes in 0 blocks
==1213== indirectly lost: 0 bytes in 0 blocks
==1213== possibly lost: 0 bytes in 0 blocks
==1213== still reachable: 568 bytes in 1 blocks
==1213== suppressed: 0 bytes in 0 blocks
==1213== Rerun with --leak-check=full to see details of leaked memory
==1213==
==1213== For counts of detected and suppressed errors, rerun with: -v
==1213== ERROR SUMMARY: 3 errors from 1 contexts (suppressed: 0 from 0)
任何可能导致此问题的提示？
答案 0 :(得分：2)
这是你的问题：
strBuffer = realloc(strBuffer, numEx);
如果对realloc()的调用失败，则返回空指针，但不释放原始内存分配。
您需要先检查返回值，如果成功则将其分配给原始指针：
char *tmpBuffer = realloc(strBuffer, numEx);
if (!tmpBuffer) {
free(strBuffer);
puts("realloc() failed");
exit(1);
}
else {
strBuffer = tmpBuffer;
}
您的代码还有其他一些问题，包括：
如果strBuffer为NULL，则无法将其传递给free（）。
sizeof()不是运行时函数，所以它不知道分配了多少内存。
strBuffer = malloc(sizeof(char)*maxS+1);有点草率。我认为你的意思是strBuffer = malloc(sizeof(char)*(maxS+1));，但你可以放strBuffer = malloc(maxS+1);，因为根据定义，sizeof(char)是1。
答案 1 :(得分：2)
嗯，到目前为止，每个人都给了你非常重要的建议，你应该考虑使用它们（主要是tempBuffer）。但问题是您忘记关闭文件描述符：
fclose(fd);
此外，sizeof是编译时，因此无法为您提供动态分配的内存大小，而strlen需要\n个字符才能工作。计算分配和释放的内存是一项艰巨的任务，它的解决方案并非如此简单。
我执行了您更新的代码，我只从1个上下文中 1个错误，可以通过更改以下行来解决：
tmpBuffer = realloc(strBuffer, numEx + 1);
除此之外， fclose（fd）之后的所有内存都是免费的。我在使用gcc 4.8.1的Ubuntu 12.04机器上。
答案 2 :(得分：1)
while((c=fgetc(fd) != EOF))应为while((c=fgetc(fd)) != EOF)。结果是，您尝试将1存储在字符串中而不是您阅读的字符中。
内存问题源于strlen(strBuffer);。您正在对不是以空字符结尾的字符串调用strlen，这会导致未定义的行为。 （这显示为valgrind报告说＆＃34; strlen中的大小为1的读取无效）。
要解决此问题，请删除strlenSize并执行：
maxS = 2 * maxS;
strBuffer = realloc(strBuffer, maxS + 1);
请注意，如果您想要＆＃34;清洁＆＃34; valgrind在你内存不足的情况下，你需要检查realloc的返回值，然后再将其分配给strBuffer，因为squeamish ossifrage指出。
NB。您的错误处理代码很差。 sizeof(strBuffer)找到指针的大小。您要打印的值为maxS。此外，free(NULL)没有效果;并且在您调用else的块后面没有exit()块。
答案 3 :(得分：1)
this compiles, and does the job
it includes error handling
it eliminated many meaningless variables
it eliminates the errors in the logic of the OPs code
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
int main()
{
int maxS = 200; // current allocation size
char *strBuffer = NULL;
if( NULL == (strBuffer = malloc(maxS) ) )
{ // then, malloc failed
perror( "malloc failed" );
exit(99);
}
// implied else, malloc successful
printf("Alocated: %d Bytes of memory.\n", )maxS+1));
// file opening simulation
FILE* fd = fopen("a", "r");
if(fd == NULL)
{ // then fopen failed
perror( "fopen failed for file: a" );
free(strBuffer);
exit(99);
}
// implied else, fopen successful
int c; // receives input char from fgetc()
int fcv = 0; // index into malloc'd memory
// tmpBuffer used in realloc()
// so will not lose pointer to already allocated memory
// in case realloc() fails
char *tmpBuffer;
while((c=fgetc(fd)) != EOF)
{
strBuffer[fcv] = c;
fcv++;
if(fcv >= maxS)
{
printf("Additional memory space required!\n");
if( NULL == ()tmpBuffer = realloc(strBuffer, 2*maxS) )
{
perror( "realloc failed" );
free(strBuffer);
fclose(fd);
exit(99);
}
// implied else, realloc successful
maxS *= 2; // only update after being sure realloc successful
strBuffer = tmpBuffer;
printf("Reallocation successful!\n");
printf("Allocated: %d Bytes of memory.\n", maxS);
} // end if
} // end while
free(strBuffer);
fclose(fd);
printf("Freed %d bytes of memory!\n", maxS);
return( 0 );
} // end function: main