嘗試將輸入解析為令牌時，malloc 校驗和錯誤不正確

Question

我正在嘗試創建一個 shell，但我一直遇到錯誤，

malloc：已釋放對象的校驗和不正確

在我的代碼以及測試時的分段錯誤中，是否有可能的解決方法？ 我試過調試，但在代碼中找不到任何異常，有人可以指出我正確的方向嗎？

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;
}

Answer 1

count初始化為 0，然后使用args[count]賦值似乎是問題所在。

getArguments()函數最初為參數創建一個單項數組，但隨后分配count = 0 - 這應該是1 ，因為存在第一個元素。

接下來，代碼使用count的全長進行賦值。 顯然，在 C 中，數組的索引從0到length-1 ，因此my_array[ length ]永遠不會正確。

只需將count初始化為 1 並將數組索引固定為 0-offset 即可解決問題。

/* 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;
}

示例輸出（通過 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)

也許您的代碼被指示使用realloc()作為賦值或類似的東西，但更簡單的方法是簡單地計算參數的數量，將args分配到正確的大小（完成一次），從而不進行循環解析重新分配。