我正在努力补充我的 C 内存管理知识。我的背景主要是脚本编写和管理,我想了解更多有关 C 和 C++ 的知识。为此,我读了几本书,其中包括使用 realloc
修剪一串空格的示例:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
char* trim(char* phrase)
{
char* old = phrase;
char* new = phrase;
while(*old == ' ') {
old++;
}
while(*old) {
*(new++) = *(old++);
}
*new = 0;
return (char*)realloc(phrase, strlen(phrase)+1);
}
int main ()
{
char* buffer = (char*)malloc(strlen(" cat")+1);
strcpy(buffer, " cat");
printf("%s\n", trim(buffer));
free(buffer);
buffer=NULL;
return 0;
}
我忠实地复制了示例,并使用 c99 -Wall -Wpointer-arith -O3 -pedantic -march=native
编译。我没有遇到任何编译错误,并且该应用程序运行并按照书中所 promise 的进行,但是当我针对 valgrind 运行它时,我收到有关无效 realloc
的错误。
==21601== Memcheck, a memory error detector
==21601== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
==21601== Using Valgrind-3.10.0.SVN and LibVEX; rerun with -h for copyright info
==21601== Command: ./trim
==21601==
==21601== Invalid free() / delete / delete[] / realloc()
==21601== at 0x402B3D8: free (in /usr/lib/valgrind/vgpreload_memcheck-x86-linux.so)
==21601== by 0x804844E: main (in /home/mo/programming/learning_pointers/trim)
==21601== Address 0x4202028 is 0 bytes inside a block of size 6 free'd
==21601== at 0x402C324: realloc (in /usr/lib/valgrind/vgpreload_memcheck-x86-linux.so)
==21601== by 0x80485A9: trim (in /home/mo/programming/learning_pointers/trim)
==21601== by 0x804842E: main (in /home/mo/programming/learning_pointers/trim)
==21601==
==21601==
==21601== HEAP SUMMARY:
==21601== in use at exit: 4 bytes in 1 blocks
==21601== total heap usage: 2 allocs, 2 frees, 10 bytes allocated
==21601==
==21601== 4 bytes in 1 blocks are definitely lost in loss record 1 of 1
==21601== at 0x402C324: realloc (in /usr/lib/valgrind/vgpreload_memcheck-x86-linux.so)
==21601== by 0x80485A9: trim (in /home/mo/programming/learning_pointers/trim)
==21601== by 0x804842E: main (in /home/mo/programming/learning_pointers/trim)
==21601==
==21601== LEAK SUMMARY:
==21601== definitely lost: 4 bytes in 1 blocks
==21601== indirectly lost: 0 bytes in 0 blocks
==21601== possibly lost: 0 bytes in 0 blocks
==21601== still reachable: 0 bytes in 0 blocks
==21601== suppressed: 0 bytes in 0 blocks
==21601==
==21601== For counts of detected and suppressed errors, rerun with: -v
==21601== ERROR SUMMARY: 2 errors from 2 contexts (suppressed: 0 from 0)
所以请帮助我理解为什么它被认为是无效的重新分配。这个例子是废话吗?有什么我想念的吗?我知道根据规范,realloc 期望指针先前已由 malloc 创建,这是因为 realloc 在另一个函数中吗?还是因为 valgrind 在不同的函数中而感到困惑?我不是一个彻头彻尾的白痴(大多数时候),但现在我有点像一个没有看到问题的人。
提前致谢!
最佳答案
您正在尝试释放
原始指针,而不是realloc
d 指针。您可以通过以下方式修复它:
buffer = trim(buffer)
关于c - Valgrind 报告无效的 Realloc,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/24458075/