Thread: having some trouble calling a function in the main program

Hi everyone. I'm writing this program that takes a sentence and breaks it up into words and spits that out in a vertical column. I couldn't use the "strtok" function so I wrote one from scratch. Anyways, I believe I wrote it correctly and now I'm trying to call it into the program. I have to be honest, I don't have much knowledge on functions especially when pointers are involved. Can anyone explain what I should be doing?

Code:

#include <stdio.h>
#include <string.h>
#define MAXLENGTH 256

char * next_word(char *instring, char **new_start);

int main ()
{
	char buffer[MAXLENGTH];
	

	printf("Enter text of line");

	while (1)
	{
		fgets(buffer, MAXLENGTH, stdin);
		if (buffer[0] == '\n')
			break;
		
                puts(buffer);
		//need help with what to do here
		next_word(buffer, MAXLENGTH);
	        
		return 0;
	}
}


char *next_word(char *instring, char **new_start)
{
	char *token;

	if(instring == NULL)
		instring=*new_start;

	instring += strspn(instring, '\0');
	if (*instring == '\0');
	return NULL;

	token = instring;
	instring = strpbrk(token, '\0');
	if (instring = NULL)
	{
		*new_start = strchr(token, '\0');
	}
	else
	{
		*instring = '\0';
		*new_start= instring +1;
	}
	return token;
}

Originally Posted by Sebastiani

>> next_word(buffer, MAXLENGTH);

Why are you passing an integer as the second parameter? Form a pointer to buffer, and pass the address of that pointer. Also, you'll probably want to call next_word in a loop.

Finally, before you go any further, try printing the values of variables at various points of execution to see what's going on:

Code:

char *next_word(char *instring, char **new_start)
{
	char *token;

	if(instring == NULL)
		instring=*new_start;

	printf("Address of instring: %x\n", instring);
	printf("Address of newstart: %x\n", *new_start);

	instring += strspn(instring, '\0');

	printf("Address of instring after strspn: %x\n", instring);
	
	if (*instring == '\0');
	return NULL;

	token = instring;
	instring = strpbrk(token, '\0');

	printf("Address of instring after strpbrk: %x\n", instring);

	if (instring = NULL)
	{
		*new_start = strchr(token, '\0');
	}
	else
	{
		*instring = '\0';
		*new_start= instring +1;
	}
	return token;
}

yeah honestly I had no idea what I was doing with calling the function. Now I feel like my strtok code isnt going to work properly Is there a way I can test it without calling it into the main program?

Okay I think I got it, but it gives me the assignment makes integer from pointer w/o cast error. Also, I believe Im getting a segmentation fault after I type in my sentence.

Code:

#include <stdio.h>
#include <string.h>
#define MAXLENGTH 256

//function portotype
char * next_word(char *instring, char **new_start);


int main ()
{
	char instring[MAXLENGTH];
	int words;
	char *parsed=NULL;

	printf("Enter text of line");

	while (1)
	{
		fgets(instring, MAXLENGTH, stdin);
		if (instring[0] == '\n')
			break;
		
		//puts(instring);

		//need help with what to do here
		words=next_word(instring, &parsed);
		
		
		return 0;
	}
}


char *next_word(char *instring, char **new_start)
{
	char *token;

	if(instring == NULL)
		instring=*new_start;

	//printf("Adress of instring: %x\n", instring);
	//printf("Addres of newstart: %x\n", *new_start);
	
	instring += strspn(instring, '\0');
	
	//printf("Address of instring after strspn: %x\n", instring);

	if (*instring == '\0');
	return NULL;

	token = instring;
	instring = strpbrk(token, '\0');

	//printf("Address of instring after strpbrk: %x\n", instring);

	if (instring = NULL)
	{
		*new_start = strchr(token, '\0');
	}
	else
	{
		*instring = '\0';
		*new_start= instring +1;
	}
	return token;
}

Originally Posted by Sebastiani

>> char *parsed=NULL;

It crashes because the code dereferenced a NULL pointer. Set it to the address of the buffer. And don't comment out the print statements (and in fact, add more, as necessary), they'll help pinpoint what the program is doing before it crashes.

so char* parsed=instring;?
Ill definitely be uncommenting the print statements once this program makes it to that point lol

Originally Posted by Sebastiani

>> I couldn't use the "strtok" function so I wrote one from scratch.

Does the function have to work like strtok (as in "is that part of the assigment?"), because if not, I would recommend a different approach. strtok is a sloppy function IMO (and uses static variables internally, which creates various problems), and you could probably do much better than that with a more simple, straightforward function.

It does not have to work like strtok, thats the only thing i could find to get me started. The only requirement is it have this function:

char *next_word(char *instring, char **new_start)

Do you have any ideas for a simpler approach? Everything I researched referred to the strtok function, including the book im using.

Im going to try to finish the current program since it seems like im having trouble even using the strtok function. I fixed the compiling errors that i was receiving, but im still segfaulting when I run the program.

Code:

#include <stdio.h>
#include <string.h>
#define MAXLENGTH 256

//function portotype
char * next_word(char *instring, char **new_start);


int main ()
{
	char instring[MAXLENGTH];
	char *words;
	char *parsed=NULL;

	printf("Enter text of line");

	while (1)
	{
		fgets(instring, MAXLENGTH, stdin);
		if (instring[0] == '\n')
			break;
		
		//puts(instring);

		//need help with what to do here
		words=next_word(instring, &parsed );
		
		
		return 0;
	}
}


char *next_word(char *instring, char **new_start)
{
	char *token;

	if(instring == NULL)
		instring=*new_start;

	printf("Adress of instring: %x\n", instring);
	printf("Addres of newstart: %x\n", *new_start);
	
	instring += strspn(instring, '\0');
	
	printf("Address of instring after strspn: %x\n", instring);

	if (*instring == '\0')
	{
	return NULL;
	}

	token = instring;
	instring = strpbrk(token, '\0');

	printf("Address of instring after strpbrk: %x\n", instring);

	if (instring = NULL)
	{
		*new_start = strchr(token, '\0');
	}
	else
	{
		*instring = '\0';
		*new_start= instring +1;
	}
	return token;
}

Am I still dereferencing a null pointer?