使用memcpy〔closed〕获取分段错误

我有点麻烦 malloc 、指针数组和 memcpy 。我有一个名为hex_string的字符串,它的长度总是可以被8整除。我正在尝试将该字符串拆分为子字符串,每个子字符串包含8个字符。当字符串中有16个字符时,这很好,但如果我将其增加到24个字符或更多,则会出现分段错误。有人能帮我吗?我知道我使用了很多for循环,这些循环基本上运行同一个循环,我将浓缩这些循环,但我想先单独完成程序的每个部分。

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] = '\0';
    }

    /* 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;
}