Question

The following piece of code gives a segmentation fault when allocating memory for the last arg. What am I doing wrong? Thanks.

    int n_args = 0, i = 0;
    while (line[i] != '\0')
    {
        if (isspace(line[i++]))
            n_args++;
    }

    for (i = 0; i < n_args; i++)
        command = malloc (n_args * sizeof(char*));

    char* arg = NULL;
    arg = strtok(line, " \n");
    while (arg != NULL)
    {
        arg = strtok(NULL, " \n");
            command[i] = malloc ( (strlen(arg)+1) * sizeof(char) );
        strcpy(command[i], arg);
        i++;
    }

Thanks.

Answer 1

You don’t reset the value of i after the for loop, so i is equal to n_args when you reach the bottom block. Trying to access command[i] at that point accesses uninitialized memory and segfaults.

The real lesson here is not to reuse variables in this manner without a good reason. Your code will be more robust and easier to read if you use something other than i in the middle for loop.