来自 Valgrind 日志的 malloc 内存泄漏

Question

我正在进行 CS50 练习：许可证。这段代码是从txt文件中读取车牌并打印出来。 有人可以帮我知道为什么我的代码仍然存在内存泄漏吗？ 我仍然收到来自 Valgrind 的这条消息：

==11625== 448 bytes in 8 blocks are definitely lost in loss record 1 of 1
==11625==    at 0x4848899: malloc (in /usr/libexec/valgrind/vgpreload_memcheck-amd64-linux.so)
==11625==    by 0x109227: main (license.c:29)
==11625== 
==11625== LEAK SUMMARY:
==11625==    definitely lost: 448 bytes in 8 blocks
==11625==    indirectly lost: 0 bytes in 0 blocks
==11625==      possibly lost: 0 bytes in 0 blocks
==11625==    still reachable: 0 bytes in 0 blocks
==11625==         suppressed: 0 bytes in 0 blocks
==11625== 
==11625== For lists of detected and suppressed errors, rerun with: -s
==11625== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 0 from 0)

我以为我已经用这段代码释放了之前由 malloc 声明的所有内存：

while (idx < 8)
{
    free(plates[idx]);
    idx ++;
}

这是完整代码

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

int main(int argc, char *argv[])
{
    // Check for command line args
    if (argc != 2)
    {
        printf("Usage: ./read infile\n");
        return 1;
    }

    // Create buffer to read into
    char buffer[7];

    // Create array to store plate numbers
    char *plates[8];

    FILE *infile = fopen(argv[1], "r");

    int idx = 0;

    while (fread(buffer, 1, 7, infile) == 7)
    {
        // Replace '\n' with '\0'
        buffer[6] = '\0';
        plates[idx] = malloc (7 * sizeof(char *));

        // Save plate number in array
        strcpy(plates[idx], buffer);
        idx++;
    }

    for (int i = 0; i < 8; i++)
    {
        printf("%s\n", plates[i]);
    }

    //free memory
    fclose(infile);
    while (idx < 8)
    {
    free(plates[idx]);
    idx ++;
    }
    return 0;
}

Answer 1

这是我的代码

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

int main(int argc, char *argv[])
{
    // Check for command line args
    if (argc != 2)
    {
        printf("Usage: ./read infile\n");
        return 1;
    }

    // Create buffer to read into
    char buffer[7];

    // Create array of character pointers to store plate numbers
    char *plates[8];

    // create a file pointer to our external text file
    FILE *infile = fopen(argv[1], "r");

    int idx = 0;

    while (fread(buffer, 1, 7, infile) == 7)
    {
        // Replace '\n' with '\0' turning it into a string
        buffer[6] = '\0';

        // allocate memory to store a string of the same length as buffer
        plates[idx] = malloc(strlen(buffer) + 1);

        // check if memory allocation was successful
        if (plates[idx] == NULL)
        {
            fprintf(stderr, "Memory allocation failed\n");
        }
        // Copy plate number to allocated memory
        strcpy(plates[idx], buffer);
        idx++;
    }

    for (int i = 0; i < idx; i++)
    {
        printf("%s\n", plates[i]);

        // Free the allocated memory for each plate number
        free(plates[i]);
    }
    // Close the file
    fclose(infile);

    return 0;
}