内存已分配但无法释放 C

Question

我目前正在C中进行一个项目，我的目标是创建一个字符串数组，并用文件中的单词填充所有字符串(目前我只是显式插入一个字符串(。

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
int main(){

int numLetters = 4;
/* The Amount of words in each file, File 1, 2, 3 */
int totalWordQuantity = 19829; 
/*the word that we test, we add by two because first 4: word, 5th: n, 6th: */
char word[numLetters + 1]; 
/*how many times we've changed the character*/
int letterSpot = 0; 
/*the character that goes through the file*/
char c; 

char* wordDocuments[3] = {"WordDocuments/Two_Letter_Connections.txt", "WordDocuments/Three_Letter_Connections.txt", "WordDocuments/Four_Letter_Connections.txt"};
/*Four Letter Word Document*/
FILE *flwd = fopen(wordDocuments[numLetters - 2], "r"); 
if(flwd == NULL){
printf("Cold Dog.");
} 
/* P is a step ahead of c, because otherwise the words get super messed up. */
char p = fgetc(flwd); 
c = p; 

/*This stores all of the words*/
char** wordStorage = (char**)calloc(totalWordQuantity, sizeof(char*) * (numLetters + 1));
int wordCount = 0; 
int i;
for(i = 0; i < totalWordQuantity; i++){
wordStorage[i] = malloc(sizeof(char) * (numLetters + 1)); 
}
/* First, take the character */
while((c = p) != EOF){
p = fgetc(flwd);
if((c == ' ' && p != 'n') || c == 'n'){
strcpy(wordStorage[wordCount], "pies");  
wordCount++;
}
c = p;
}

for(i = 0; i < totalWordQuantity; i++){
free(wordStorage[i]); 
}

free(wordStorage);

fclose(flwd); 
return 0; 
}

此代码没有收到任何编译问题，并且运行良好；然而，当我运行它时，valgrind给了我一个错误：

==29== Memcheck, a memory error detector
==29== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==29== Using Valgrind-3.15.0 and LibVEX; rerun with -h for copyright info
==29== Command: ./flwp
==29==
==29== error calling PR_SET_PTRACER, vgdb might block
==29== Invalid write of size 4
==29==    at 0x109419: main (in /mnt/c/Users/Jordan/Documents/GitHub/flwg/flwp)
==29==  Address 0x0 is not stack'd, malloc'd or (recently) free'd
==29==
==29==
==29== Process terminating with default action of signal 11 (SIGSEGV)
==29==  Access not within mapped region at address 0x0
==29==    at 0x109419: main (in /mnt/c/Users/Jordan/Documents/GitHub/flwg/flwp)
==29==  If you believe this happened as a result of a stack
==29==  overflow in your program's main thread (unlikely but
==29==  possible), you can try to increase the size of the
==29==  main thread stack using the --main-stacksize= flag.
==29==  The main thread stack size used in this run was 8388608.
==29==
==29== HEAP SUMMARY:
==29==     in use at exit: 892,777 bytes in 19,831 blocks
==29==   total heap usage: 19,832 allocs, 1 frees, 896,873 bytes allocated
==29==
==29== LEAK SUMMARY:
==29==    definitely lost: 0 bytes in 0 blocks
==29==    indirectly lost: 0 bytes in 0 blocks
==29==      possibly lost: 0 bytes in 0 blocks
==29==    still reachable: 892,777 bytes in 19,831 blocks
==29==         suppressed: 0 bytes in 0 blocks
==29== Reachable blocks (those to which a pointer was found) are not shown.
==29== To see them, rerun with: --leak-check=full --show-leak-kinds=all
==29==
==29== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 0 from 0)
==29==
==29== 1 errors in context 1 of 1:
==29== Invalid write of size 4
==29==    at 0x109419: main (in /mnt/c/Users/Jordan/Documents/GitHub/flwg/flwp)
==29==  Address 0x0 is not stack'd, malloc'd or (recently) free'd
==29==
==29== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 0 from 0)
Segmentation fault (core dumped)

Dr。当我试图运行它时，内存崩溃。如果我将while循环和其中的所有行替换为：，它就可以工作，不会出现任何内存问题

for(int i = 0; i < totalWordQuantity; i++){
strcpy(wordStorage[wordCount], "word"); 
}

如有任何帮助或建议，我们将不胜感激！非常感谢。

Answer 1

标题有点误导。问题似乎不是内存泄漏，即已分配但从未释放的内存，而是非法的内存访问。

也许问题只是因为路径不正确(因为您似乎使用的是Cygwin的Valgrind(，但由于错误处理不当，您无法看到它。

if(flwd == NULL){
printf("Cold Dog.");
} 

在这里，程序继续执行，尽管文件没有成功打开。由于stdout是缓冲的，所以在我的机器上我无法看到错误并获得SEGFAULT。

if(flwd == NULL){
fprintf( stderr, "Cold Dog.");
exit(EXIT_FAILURE);
} 

还有一些其他问题：

char** wordStorage = (char**)calloc(totalWordQuantity, sizeof(char*) * (numLetters + 1));

你在这里分配的空间太多了。您应该分配totalWorldQuantity乘以sizeof char指针(char*(。

char** wordStorage = (char**)calloc(totalWordQuantity, sizeof(char*));

但这不应该引起任何问题，除了过度分配。

char p = fgetc(flwd); 

应该是

int p = fgetc(flwd); 

否则，非EOF字符可能被解释为EOF。