使用 free() 无法释放内存

Question

我无法释放使用 malloc 分配的内存。该程序运行良好，直到它应该使用 free 释放内存的部分。程序在这里冻结。所以我想知道问题可能出在哪里，因为我只是在学习 C。从语法上看，代码似乎是正确的，所以我是否需要在从该位置或其他位置释放内存之前删除该位置的所有内容？

这是代码。

// Program to accept and print out five strings
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define NOOFSTRINGS 5
#define BUFFSIZE 255

int main()
{
    char buffer[BUFFSIZE];//buffer to temporarily store strings input by user
    char *arrayOfStrngs[NOOFSTRINGS];
    int i;

    for(i=0; i<NOOFSTRINGS; i++)
    {
        printf("Enter string %d:\n",(i+1));
        arrayOfStrngs[i]=(char*)malloc(strlen(gets(buffer)+1));//calculates string length and allocates appropriate memory
        if( arrayOfStrngs[i] != NULL)//checking if memory allocation was successful
        {
            strcpy(arrayOfStrngs[i], buffer);//copies input string srom buffer to a storage loacation
        }
        else//prints error message and exits
        {
            printf("Debug: Dynamic memory allocation failed");
            exit (EXIT_FAILURE);
        }
    }

    printf("\nHere are the strings you typed in:\n");
    //outputting all the strings input by the user
    for(i=0; i<NOOFSTRINGS; i++)
    {
        puts(arrayOfStrngs[i]);
        printf("\n");
    }

    //Freeing up allocated memory
    for(i=0; i<NOOFSTRINGS; i++)
    {
        free(arrayOfStrngs[i]);
        if(arrayOfStrngs[i] != NULL)
        {
            printf("Debug: Memory deallocation failed");
            exit(EXIT_FAILURE);
        }
    }

    return 0;
}

Answer 1

你误用了strlen()，这会导致缓冲区溢出：

arrayOfStrngs[i]=(char*)malloc(strlen(gets(buffer)+1)); //pointer from gets() is incremented and passed to strlen()  - that's wrong

应该是

arrayOfStrngs[i]=(char*)malloc(strlen(gets(buffer))+1); //pointer from gets() is passed to strlen(), then returned value is incremented - correct

free() 也不会更改传递给它的指针。这样

 char* originalValue = pointerToFree;
 free( pointerToFree ); 
 assert( pointerToFree == originalValue ); //condition will always hold true

所以在你的代码中释放内存应该只是

//Freeing up allocated memory
for(i=0; i<NOOFSTRINGS; i++)
{
    free(arrayOfStrngs[i]);
}

Answer 2

arrayOfStrngs[i]=(char*)malloc(strlen(gets(buffer)+1));//calculates string length and allocates appropriate memory

不应该是这样的

arrayOfStrngs[i]=(char*)malloc(strlen(gets(buffer))+1);