C: seg fault: using strtok

[deathmetal]

Hi members,
I'm fairly new to C programming. I've worked in python, and bash.

I want to split string and store it in an array:

Function takes: character array, and the words in it.

void array_of_str(char *line, unsigned int count){                                                                                                                                             
  unsigned int i=0;                                                                                                                                                                            
  char *array[count];                                                                                                                                                                          
  char *p;                                                                                                                                                                                     
  p=strtok(line,'\t');                                                                                                                                                                         
                                                                                                                                                                                               
  while(p !=NULL){                                                                                                                                                                             
    printf("Value of I is %d\n",i);                                                                                                                                                            
    array[i++]=p;                                                                                                                                                                              
    p=strtok(NULL,'\t');                                                                                                                                                                       
  }                                                                                                                                                                                            
  printf("##--##\n");                                                                                                                                                                          
}

I compile my code as:

gcc -g -Wall -Wextra *.c -o program_parse -std=gnu99

I get warnings as:

 warning: implicit declaration of function ‘strtok’ [-Wimplicit-function-declaration]
   p=strtok(line,'\t');
warning: assignment makes pointer from integer without a cast
p=strtok(NULL,'\t');

In my headers in main file, I've:

#define _GNU_SOURCE
#include<string.h>

When I run my code, i get error:

Segmentation fault (core dumped)

String I'm passing:

denovo2819 A15_94875 B13_87655 B23_17316

count=4

Unable to solve this.
Any help would be appreciated.
thanks.

[kmdv]

#include <string.h> must appear before the use of strtok(). It probably is not included at all (check your headers).

By the way, "char *array[count]" in your function is unused.

[laserlight]

This:

p=strtok(line,'\t');

should have been:

p = strtok(line, "\t");

Notice the second argument.

You should #include <string.h> in the file containing the definition of array_of_str, not just in the file containing the definition of the main function.

[jimblumberg]

Did you fix those warnings? Running a program that compiled with warnings you don't understand is asking for trouble. Those warnings are very serious problems. The first problem is that you forgot to #include the proper header file that defines strtok(). The second error is related to the first.

Also I would recommend changing your compile line a little:

gcc -g -Wall -Wextra -pedantic -pendantic-errors Wvla *.c -o program_parse -std=C99

This will force gcc to avoid using any compiler specific "features" and use the C99 standard features only.

Jim

[deathmetal]

#include <string.h> must appear before the use of strtok(). It probably is not included at all (check your headers).

Hi,
Thanks for your reply.
<string.h> is included before calling strtok.
Also,

denovo2819 A15_94875 B13_87655 B23_17316

is a character array not string

[jimblumberg]

is a character array not string

But remember strtok() requires a string not an array of char.

Jim

[laserlight]

<string.h> is included before calling strtok.

No, it isn't: your compiler warning about "implicit declaration of function ‘strtok’" says otherwise.

Also,

denovo2819 A15_94875 B13_87655 B23_17316

is a character array not string

What do you mean? Just show an example call of array_of_str, and remember to fix the calls to strtok that I mentioned.

[deathmetal]

Hi laserlight,

Thanks for your reply.
I've

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

#define _GNU_SOURCE
#include<string.h>

#include "parse_files.h"

This doesn't fix strtok warning for some reason.

gcc -v

Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/apps/gcc/4.9.2/libexec/gcc/x86_64-unknown-linux-gnu/4.9.2/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: ./configure --prefix=/apps/gcc/4.9.2
Thread model: posix
gcc version 4.9.2 (GCC)

char line[100];
/*
read file. Get rid of \n
put '\0' at the end

*/
/*
get_tab_count - gives you word count
*/
array_of_str(line,get_tab_count(line)+1);

void array_of_str(char *line, unsigned int count){
  unsigned int i=0;

  char *p;
  printf("where are you??\n");
  p=strtok(line,'\t');

  while(p !=NULL){
    printf("Value of I is %d\n",i);  
    /*array[i++]=p;*/
    p=strtok(NULL,'\t');
  }
  printf("##--##\n");
}
/**/

Could this be reason:
c - strtok giving Segmentation Fault - Stack Overflow

s[]="Test to pass strtok()"; /* this can be passed to strtok() */

char *m="Test to pass strtok()"; /* passing this will result in SIGSEGV */



strtok is not being recongized despite adding string.h.
Why?

[deathmetal]

if I include string.h anywhere else and compile, I get warnings as:

/usr/include/string.h:348:14: note: expected ‘const char * restrict’ but argument is of type ‘int’
extern char *strtok (char *__restrict __s, __const char *__restrict __delim)
^
parse_files.c:64:19: warning: passing argument 2 of ‘strtok’ makes pointer from integer without a cast
p=strtok(NULL,'\t');
^
In file included from parse_files.h:5:0,
from parse_files.c:4:
/usr/include/string.h:348:14: note: expected ‘const char * restrict’ but argument is of type ‘int’
extern char *strtok (char *__restrict __s, __const char *__restrict __delim)

[laserlight]

This doesn't fix strtok warning for some reason.

I don't see the definition of array_of_str, so maybe you got the wrong file.
Temporarily change this:

void array_of_str(char *line, unsigned int count){

to:

#include <string.h>

void array_of_str(char *line, unsigned int count){

Compile. The warning should be gone. You can then move that include to where the includes normally are.

Could this be reason:

No, because line is a modifiable array.

It looks like you still have not fixed this:

p=strtok(line,'\t');

Neither have you fixed this:

p=strtok(NULL,'\t');

[deathmetal]

Hi,
Thank you for pointing out to the error. Finally it got fixed. Compiler was annoyed with:

p=strtok(line,'\t');

in stead of:

p=strtok(line,"\t");

Thanks again for your help and guiding.

[Salem]

> Compiler was annoyed with:
Blaming the compiler for pointing out your programming mistake - whatever next....

[tonyp12]

'\t' is not even close to how it sees "\t"

' ' is normally only used for char and I'm not even sure how it handles escape and also it does not add a zero byte at the end.
" " compiler places the string in const segment and add a zero to the end and give you a pointer to the location

Zero at the end is something strtok() needs as you don't parse for just a char but it expects a (char *) string pointer (even if you just need one byte)