Something

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

char *InnerAdd(const char *message, va_list params)
{
	char mask[] = "%s\r\n";

	size_t length = vsnprintf(NULL, 0, mask, params);
	//char *final = (char *) malloc((length + 1) * sizeof(char));
	char *final = (char *) malloc(1024);
	int result = vsnprintf(final, length + 1, mask, params);

	printf("vsnprintf result: %d\r\n", result);
	printf("%s", final);

	return final;
}

char *AddLine(const char *message, ...)
{
	va_list va_args;
	va_start(va_args, message);
	InnerAdd(message, va_args);
	va_end(va_args);
}

int main(int argc, char **argv)
{
	char message[] = "This is a test.";

	if (strcmp(AddLine(message), "This is a test.\r\n") != 0)
	{
		printf("Test failure!\r\n");
	}
	else
	{
		printf("Test succeeded.\r\n");
	}

	return 0;
}