segmentation fault from strtok

Question

im trying a simple program that will read a string, a capital letter, and 2 floats from input.

no matter how much i debug, change, or check the code or input, i keep getting segmentation fault at the last token read.

the input i enter is: text A,1,2. i would like the program to ignore all white spaces and commas between the capital letter and values.

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

int main(){

   char *value, *string;
    char buffer[100];
    float x;
    if(fgets(buffer, sizeof(buffer), stdin)==NULL)
                printf("empty input\n");

    string = strtok(buffer, " ");

    if(strcmp(string, "text")==0){  
            if((value = strtok(NULL, " \t\n")!=NULL))  /*seg.falt causes here*/
                sscanf(value, " %f", &x);              /*or here*/
    }
}

if i print the value of value in the console with p value it says 0x1 <error: cannot access memory at adress 0x1 and i assume its a null pointer, but why though? the token should have 2 in it. any insights on what am i missing?

Answer 1

Compiling your program with a recent GCC produces this warning:

t.c: In function ‘main’:
t.c:15:23: warning: assignment to ‘char *’ from ‘int’ makes pointer from integer without a cast [-Wint-conversion]
   15 |             if((value = strtok(NULL, " \t\n")!=NULL))  /*seg.falt causes here*/
      |                       ^

There is a high chance that fixing the parenthesis to do what you wanted them to do will fix the crash:

if ((value = strtok(NULL, " \t\n")) != NULL)

P.S. You should get into a habit of building your programs with gcc -Wall -Wextra.