Implicit Declaration of Function ‘strtok_r’ Despite 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 **);