C file compiling but not running

Question

So my program takes a file as input and parses out spaces. Tokens are saved into an array. I have a function to print out the contents of the array to test if the parser works. The code compiles with gcc -o filename filename.c . But when I run the program and give it a filepath, I get a pop up window indicating filename.exe has stopped working : A problem caused the program to stop working correctly. Windows will close the program and notify you if a solution is available.

#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
char file_name[100];
char *token_array[256];
int main()
{
   char ch;
   FILE *fp;

   int n=0;
   char *str;

   printf("Enter filepath\n");
   gets(file_name);

   fp = fopen(file_name,"r"); 

   if( fp == NULL )
   {
      perror("Error opening the file.\n");
      exit(EXIT_FAILURE);
   }

   int i = 0;         
   char *p; 
   while( ( ch = fgetc(fp) ) != EOF )
   {
    char *fgets(char *str, int n, FILE *stream);
    p = strtok(str, " ");
    i=0;

    while(p!=NULL)
    {
        strcpy(token_array[i], p);
    }

    i++;

   }

   for(n=0;n<256;n++)
   {
      printf("%s", &token_array[n]);
   }

   return 0;
}

Answer 1

This line does nothing:

char *fgets(char *str, int n, FILE *stream);

As written, that line is nothing but a declaration of a function, probably not what you want.

If you're going to use fgets(), use fgets() alone and don't mix it with fgetc():

char str[1024];
while ( fgets( str, sizeof( str ), fp )
{
   .
   .
   .

fgets() returns NULL upon EOF or an error condition. And note that str is not a char *, it's a char array. An even better solution would be to use getline() because fgets() with a fixed-length buffer can only read entire lines that fit into the buffer. Longer lines will be split.

fgetc() returns int, not char. But you don't shouldn't use fgetc() when reading lines from a file with fgets(). Pick one and use that. But if you use fgetc(), you'll need to write code to put together each line as you read it character-by-character.

And what does token_array[i] point to? You declare token_array as an array of pointers:

char *token_array[256];

But you never allocate any memory for each pointer in the array to point to.

The easiest solution is to change

strcpy(token_array[i], p);

to

token_array[i] = strdup(p);

assuming your platform has strdup(), which is equivalent to a malloc() and strcpy() to the memory returned by malloc(), so you need to call free() on the string you get from strdup().

Your use of strtok() is wrong. See How does strtok() split the string into tokens in C? for examples of proper strtok() usage.

And since token_array is an array of char * pointers, this

printf("%s", &token_array[n]);

will take the address of the actual pointer itself, and not the string it's supposed to point to. It will then try to print out a "string" in the memory containing the pointer variable. That's won't work well. Since it's already a char *, all you need is this:

printf("%s", token_array[n]);

Answer 2

You can try this code instead. I changed your program so that it can read and tokenize the file.

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

char *trim(char *s) {
    int i = strlen(s) - 1;
    if (s[i] == '\n')
        s[i] = '\0';
    return s;
}

#define BUFFER_SIZE 100
char *token_array[256];
int main( int argc, char** argv ){

    const char *delimiter_characters = " ";
    char *filename =  malloc(BUFFER_SIZE);

    int i = 0;
    printf("Enter filepath\n");
    fgets(filename, 100, stdin);


    FILE *input_file = fopen( trim(filename), "r" );
    char buffer[ BUFFER_SIZE ];
    char *last_token;

    if( input_file == NULL ){

        fprintf( stderr, "Unable to open file %s\n", filename );

    }else{

        // Read each line into the buffer
        while( fgets(buffer, BUFFER_SIZE, input_file) != NULL ){

            // Write the line to stdout
            //fputs( buffer, stdout );

            // Gets each token as a string and prints it
            last_token = strtok( buffer, delimiter_characters );
            while( last_token != NULL ){
                //printf( "%s\n", last_token );
                token_array[i] = malloc(100);
                strcpy(token_array[i], last_token);
                i++;
                last_token = strtok( NULL, delimiter_characters );
            }

        }

        if( ferror(input_file) ){
            perror( "The following error occurred" );
        }

        fclose( input_file );

    }
    int n;
    for(n=0;token_array[n] != NULL && n<256;n++)
    {
        printf("%s", token_array[n]);
        free(token_array[n]);
    }
    free(filename);
    return 0;

}

data.txt

Hello Foo Bar
How are you?

Test

Debug/gnu
Enter filepath
data.txt
HelloFooBar
Howareyou?
Process finished with exit code 0

The contents of the array are

n[0] Hello
n[1] Foo
n[2] Bar

n[3] How
n[4] are
n[5] you?

You can see the contents of the array if you add debug info:

printf("n[%d] %s\n", n, token_array[n]);