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c - malloc 尝试将输入解析为令牌时出现错误校验和错误

问题描述

我正在尝试创建一个外壳，但我一直遇到错误，

malloc：释放对象的校验和不正确

在我的代码中以及测试时的分段错误中，是否有可能解决此问题？我尝试调试，但在代码中找不到任何异常，有人可以指出我正确的方向吗？

char **getArguments(char line[])
{
    /* Pointer to char pointer for storing arguments, initial size is 1 */
    char **args = malloc(sizeof(char *));
    /* Error handling */
    if (args == NULL)
    {
        fprintf(stderr, "Error: cannot split line.");
        exit(EXIT_FAILURE);
    }
    int count = 0;
    /* Try to parse first argument */
    char *temp = strtok(line, " \t\n\r\a");
    while (temp != NULL)
    {
        args[count] = temp;
        /* Reallocate more space for next argument */
        count++;
        char **reallocated = realloc(args, count * sizeof(char *));
        /* Error handling */
        if (reallocated == NULL)
        {
            fprintf(stderr, "Error: cannot split line.");
            exit(EXIT_FAILURE);
        }
        else
        {
            args = reallocated;
        }
        /* Move to next token */
        temp = strtok(NULL, " \t\n\r\a");
    }
    /* NULL terminate the array so that we know where's the end */
    args[count] = NULL;
    return args;
}

标签： csegmentation-faultmallocrealloc

解决方案

初始化count为 0，然后分配使用args[count]似乎是问题所在。

该getArguments()函数最初为参数创建一个单项数组，但随后分配count = 0- 这应该是1因为存在第一个元素。

接下来，代码使用全长count. 显然，在 C 中，数组被索引0到length-1，所以my_array[ length ]永远不正确。

只需初始化count为 1 并将数组索引固定为 0 偏移即可解决问题。

/* Splits the command into arguments */
char **getArguments(char line[])
{
    /* Pointer to char pointer for storing arguments, initial size is 1 */
    char **args = malloc(sizeof(char *));
    /* Error handling */
    if (args == NULL)
    {
        fprintf(stderr, "Error: cannot split line.");
        exit(EXIT_FAILURE);
    }
    int count = 1;                                                       // <-- HERE
    /* Try to parse first argument */
    char *temp = strtok(line, " \t\n\r\a");
    while (temp != NULL)
    {
        args[count-1] = temp;                                            // <-- HERE
        /* Reallocate more space for next argument */
        count++;
        char **reallocated = realloc(args, count * sizeof(char *));
        /* Error handling */
        if (reallocated == NULL)
        {
            fprintf(stderr, "Error: cannot split line.");
            exit(EXIT_FAILURE);
        }
        else
        {
            args = reallocated;
        }
        /* Move to next token */
        temp = strtok(NULL, " \t\n\r\a");
    }
    /* NULL terminate the array so that we know where's the end */
    args[count-1] = NULL;                                           // <-- HERE
    return args;
}

示例输出（通过 Valgrind）

[user@machine]> valgrind ./run_cmds 
==8173== Memcheck, a memory error detector
==8173== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==8173== Using Valgrind-3.15.0 and LibVEX; rerun with -h for copyright info
==8173== Command: ./run_cmds
==8173== 
# /bin/echo foo
foo
# /bin/echo 1 2 3 4 5 6 7 8 9 10 11 12 13 14
1 2 3 4 5 6 7 8 9 10 11 12 13 14
# ==8173== 
==8173== HEAP SUMMARY:
==8173==     in use at exit: 120 bytes in 1 blocks
==8173==   total heap usage: 24 allocs, 23 frees, 3,544 bytes allocated
==8173== 
==8173== LEAK SUMMARY:
==8173==    definitely lost: 0 bytes in 0 blocks
==8173==    indirectly lost: 0 bytes in 0 blocks
==8173==      possibly lost: 0 bytes in 0 blocks
==8173==    still reachable: 120 bytes in 1 blocks
==8173==         suppressed: 0 bytes in 0 blocks
==8173== Rerun with --leak-check=full to see details of leaked memory
==8173== 
==8173== For lists of detected and suppressed errors, rerun with: -s
==8173== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)

也许您的代码被指示realloc()用作赋值等，但更简单的方法是简单地计算参数的数量，分配args到正确的大小（完成一次），因此不会循环解析重新分配。

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