implicit declaration of function ‘strtok_r’ [-Wimplicit-function-declaration] inspite including <string.h>

Question

I have the following code to tokenize a string containing lines separated by \n and each line has integers separated by a \t:

void string_to_int_array(char file_contents[BUFFER_SIZE << 5], int array[200][51]) {
  char *saveptr1, *saveptr2;
  char *str1, *str2;
  char delimiter1[2] = "\n";
  char delimiter2[2] = " ";
  char line[200];
  char integer[200];
  int j;
  for(j = 1, str1 = file_contents; ; j++, str1 = NULL) {
    line = strtok_r(str1, delimiter1, &saveptr1);

    if (line == NULL) {
      break;
    }


    for (str2 = line; ; str2 = NULL) {
      integer = strtok_r(str2, delimiter2, &saveptr2);
      if (integer == NULL) {
        break;
      }
    }
  }
}

(Have included only the relevant function here, the complete, if required, is here.)

However, when I try to compile this code using:

gcc -m64 -std=c99 -pedantic -Wall -Wshadow -Wpointer-arith -Wcast-qual -Wstrict-prototypes -Wmissing-prototypes file_read.c

I get the following warnings:

file_read.c:49:5: warning: implicit declaration of function ‘strtok_r’ [-Wimplicit-function-declaration]
     line = strtok_r(str1, delimiter1, &saveptr1);
     ^
file_read.c:49:10: error: incompatible types when assigning to type ‘char[200]’ from type ‘int’
     line = strtok_r(str1, delimiter1, &saveptr1);
          ^
file_read.c:59:15: error: incompatible types when assigning to type ‘char[200]’ from type ‘int’
       integer = strtok_r(str2, delimiter2, &saveptr2);
               ^

Line nos 49 and 59 correspond to the strtok_r call.

As you can see, I have included string.h in my file (which is where strtok_r is declared), still I get the implicit declaration warning for strtok_r.

Any insights as to how I can remove the warning is appreciated.

I am using gcc 4.8.2 on ubuntu 14.04 64-bit desktop.

Answer 1

strtok_r is not a standard C function. You have asked for only C99 by using the -std=c99compiler flag, so the header files (of glibc) will only make the standard C99 functions in string.h available to you.

Enable extensions by using -std=gnu99 , or by defining one of the extensions, shown in the manpage of strtok , that supports strtok_r before including string.h. E.g.

#define _GNU_SOURCE
#include <string.h>

Note that the code have other problems too, strtok_r returns a char * , but you are trying to assign that to a char array in integer = strtok_r(str2, delimiter2, &saveptr2);. Your integer variable should be a char *

Answer 2

Same problem with GCC 7.4.2 on Debian

Solved using __strtok_r or -std=gnu99 or adding a protoype after includes:

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

#define BUFFER_SIZE 1024

extern char *strtok_r(char *, const char *, char **);

Answer 3

the problem is that the function strtok_r returns a pointer to char, witch you are trying to assign to an array of char, so in order to make it work you have to declare your line and integer variables as a pointer of char, then allocate the memory with malloc.

void string_to_int_array(char file_contents[BUFFER_SIZE << 5], int array[200][51]) {
  char *saveptr1, *saveptr2;

  char *str1, *str2;

  char delimiter1[2] = "\n";
  char delimiter2[] = " ";
  char *line;
  char *integer;
  int j;
  line = (char*)malloc(200);
  integer = (char*)malloc(200);
  for(j = 1, str1 = file_contents; ; j++, str1 = NULL) {
    line = strtok_r(str1, delimiter1, &saveptr1);
    printf("%s\n", line);
    if (line == NULL) {
      break;
    }
    printf("end of first\n");

    for (str2 = line; ; str2 = NULL) {
    printf("begin of second\n");
      printf("asdf%s\n", line);
      integer = strtok_r(str2, delimiter2, &saveptr2);
      if (integer == NULL) {
        break;
      }
      printf("%s\n", integer);
    }
  }
}

Answer 4

I am using 4.8.2 and ubuntu 14.04 64bit too. But I got different errors.

    incompatible types when assigning to type 'char[200]' from type 'char *' 
        line = strtok_r(str1, delimiter1, &saveptr1);
             ^

here, line is declared 'char[200]' but strtok_r returns char*.

Similar errors at line for integer = ....

To get rid of these compile errors, you can declare something like char *line;.

For the warning about implicit declaration, check this

Can I use strtok() in a Linux Kernel Module?