使用 memcpy 获取分段错误

Question

我在使用 malloc、指针数组和 memcpy 时遇到了一些问题。我有一个名为 hex_string 的字符串，它的长度总是可以被 8 整除。我试图将这个字符串拆分成子字符串，每个子字符串有 8 个字符。当我在字符串中有 16 个字符时，这工作正常，但如果我将其增加到 24 个字符或更多，我会遇到分段错误。任何人都可以帮我解决这个问题吗？我知道我使用了很多本质上运行相同循环的 for 循环，我将压缩这些但我想分别执行程序的每个部分以开始。

int main (int argc, char * argv[]) {

    const char * hex_string = "1c0111001f010100abcdef12";
    /* Using this value for hex_string fails - but if the 
    string is replaced with "1c0111001f010100" the program runs fine. */

    int string_length = strlen(hex_string);

    /* get the number of 8 character substrings needed 
    (using ceil to allow me to expand this to arbitrary length strings in the future) */
    int num_of_blocks = (int)ceil((double)string_length / 8); 

    /* allocate memory for pointers to each substring */
    char ** hex_array = (char **) malloc(num_of_blocks * sizeof(char));

    /* allocate 9 bytes for each substring 
    to allow for the 8 characters and the null-terminator. */
    for (int i = 0; i  < num_of_blocks; i++)
        hex_array[i] = (char *) malloc(9);

    /* split the strings into 8-character substrings and add a null-terminator */
    for (int i = 0; i < num_of_blocks; i++) {
            memcpy(hex_array[i], hex_string+(i*8), 8);
            (hex_array[i])[8] = '[=10=]';
    }

    /* print each substring */
    for (int i = 0; i < num_of_blocks; i++)
        printf("substring %d = %s\n",i,hex_array[i]);

    /* free the memory allocated for each substring */
    for (int i = 0; i < num_of_blocks; i++)
        free(hex_array[i]);
    /* free the memory allocated for the pointers to the substrings */
    free(hex_array);

    return 0;
}

Answer 1

主要问题是在内存分配中使用了错误的类型 - 这是一个常见错误。

// char ** hex_array = (char **) malloc(num_of_blocks * sizeof(char));
char ** hex_array = (char **) malloc(num_of_blocks * sizeof(char *));

非常同意@Matt McNabb，推荐使用以下内容。不需要演员表。更容易编码。更容易维护。在这种情况下，不太可能得到错误的类型。

pointer_variable = malloc(n * sizeof *pointer_variable);

char ** hex_array = malloc(num_of_blocks * sizeof *hex_array);

使用 memcpy 获取分段错误

Getting segmentation fault with memcpy

c

malloc

memcpy

segmentation-fault