Thread: returning strings - function.

Hello, I'm trying to "import" the perl function called "join", you can see what this function make's here. Now I have this code:

Code:

int join (char str1[], char str2[], char w, char buf[], int size) {
	int i,j;
	unsigned long totsz;
	totsz = sizeof(str1) + sizeof(str2) + sizeof(w);

	//check if space is sufficient
	if (size <= totsz)
		return 0;

	for (i=0; str1[i]; i++)
		buf[i] = str1[i];

	buf[i++] = w;
	
	for (j=0; str2[j]; j++,i++)
		buf[i] = str2[j];

	buf[i] = '\0';
	return 1;
}

int main(void) {
	char buf[1000];

	if ((join ("lala", "lele", ':',buf, sizeof(buf))) != 0)
		printf("Buf = %s\n",buf);
	else
		printf("There was an error, probaly buffer is too small\n");

	return 0;
}

Perfect it works fine, my question is, how do I make possible something like that:

Code:

char joined[100];

joined = join ("lala","lele",':',sizeof(buf));

When I try to create a string in the function, and return it it says returning temp variable don't know what, and I receive a lot of $$$$s.

It's complaining because you're statically allocating memory inside the function and then passing a pointer to it outside the function. Statically allocated memory is deallocated at the end of the function its declared in, so you'd receive an invalid pointer.

If you want to do it that way, you're gonna have to dynamically allocate memory for "buf" (i.e. use malloc(...)) and then return a pointer to it, although you'll have to remember to free(...) it when you've finished with it.

Without the cast:

Code:

C:\Cpp1.cpp(8) : error C2440: '=' : cannot convert from 'void *' to 'char *'
        Conversion from 'void*' to pointer to non-'void' requires an explicit cast

Thanks prelude.

Compile it as a C file and the error will go away.

Ok, no more errors, now, isn't there anyway my program could alone free the memory I allocated? I think I'm asking too much

Thanks again Prelude, at least until now, I won't try to create my garbage collector, the final result, and this is what I wanted is:

Code:

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

char *join (char ch, ...) {
	char *buf,*s;
	int i = 0, j = 0;
	
	va_list ap;
	va_start(ap,ch);


	//alocatte memory
	if ((buf = (char *) malloc(1000 * sizeof(*buf))) == NULL) {
		printf("Could not allocate memory\n");
		exit(1);
	}

	while(s = va_arg(ap,char*)) {
		for (j = 0; s[j]; j++)
			buf[i++] = s[j];
		buf[i++] = ch;
	}

	buf[--i] = '\0'; //delete the last ':' occurence and add \0
	
	return buf;
}

int main(void) {
	char *test;

	test = join(':',"lele","loli","loaaa","sshshsh");
	printf("%s\n",test);
	free(test);
	return 0;
}

Thank you very much.