* char数组末尾的分段错误

Question

I'm new to using C and I'm running into a problem. I want to use the following code to split-up a string input from the linux command line (something like date | ./date_split ) into an array, which I will be later accessing and modifying. The splitting works initially but I get a segmentation fault at the end. Can anyone explain what I am doing wrong?

int main()
{
   char *indate[10];
   int i= 1;
   char str[100][50];
   fgets(&str [0], 50, stdin);
   const char s[2] = " ";
   char *token;

  /* get the first token */
  token = strtok(str, s);
  indate[i] = malloc(strlen(token)+1);
  strcpy(indate[i], token);
  printf( "Array before: %s\n", indate[i]);     

 /* walk through other tokens */
 while( token != NULL )
{
  printf( "Token before: %s\n", token );

  token = strtok(NULL, s);
  indate[i] = malloc(strlen(token)+1);
  strcpy(indate[i], token);

printf( "Token2 After: %s\n", token );
printf( "Array2 After: %s\n", indate[i]);     
i++;   
}

    return(0);
}

Which gives terminal output:

Array before: Thu
Token before: Thu
Token2 After: 20
Array2 After: 20
Token before: 20
Token2 After: Oct
Array2 After: Oct
Token before: Oct
Token2 After: 11:37:56
Array2 After: 11:37:56
Token before: 11:37:56
Token2 After: EDT
Array2 After: EDT
Token before: EDT
Token2 After: 2016

Array2 After: 2016

Token before: 2016

Segmentation fault (core dumped)

Answer 1

Issues with your program: your index into the date components, i , starts at 1 instead of 0 (is a terrible variable name for this purpose) and isn't updated consistently (first entry gets overwritten); the str() array is a total mess allocation-wise (eg two dimensions, only one used); you assume the first strtok() succeeds but that might not be the case with bad input; you don't test if the subsequent strtok() calls succeed until after you've already used the result; you make no attempt to free() the memory you malloc() and even lose track of some.

Below is a rework of your original code that also adds some error checking and other niceties:

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

#define MAXIMUM_TOKENS 16
#define MAXIMUM_TOKEN_LENGTH 32

const char *separator = " ";

int main()
{
    char string[(MAXIMUM_TOKEN_LENGTH + strlen(separator)) * MAXIMUM_TOKENS + 1]; // estimate

    char *result = fgets(string, sizeof(string), stdin);

    if (result == NULL)
    {
        fprintf(stderr, "An appropriate error message goes here.\n");
        return EXIT_FAILURE;
    }

    /* strip final newline (\n) if present */
    size_t last_index = strlen(string) - 1;

    if (string[last_index] == '\n')
    {
        string[last_index] = '\0';
    }

    /* get the first token */
    char *token = strtok(string, separator);

    char *date_parts[MAXIMUM_TOKENS];
    int date_parts_index = 0;

    /* walk through other tokens */
    while (token != NULL)
    {
        date_parts[date_parts_index++] = strdup(token);
        token = strtok(NULL, separator);
    }

    /* print the tokens and free the strdup/malloc memory */
    for (int i = 0; i < date_parts_index; i++)
    {
        (void) puts(date_parts[i]);
        free(date_parts[i]);
    }

    return EXIT_SUCCESS;
}

USAGE

% date | ./a.out
Thu
Oct
20
09:58:00
PDT
2016
% 

Although this is an appropriate use of strtok() , be wary of it. It is an artifact of an earlier age and should be avoided in favor of safer, modern library functions like strsep() and strtok_r() .

Answer 2

From strtok() manual

RETURN VALUE The strtok() and strtok_r() functions return a pointer to the next token, or NULL if there are no more tokens.

Once there are no more tokens, token contains a NULL pointer, and therefore strlen(token) seg faults. See strlen not checking for NULL