SDL TextInput Tutorial confusing to me

SDL Development
1

So I’m trying to create an application that has user text input, so I went to this link: https://wiki.libsdl.org/Tutorials/TextInput and followed what’s in there but I still seems to be missing something. :confounded:

This is my code:

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

#include <SDL2/SDL.h>

extern void InitVideo();
extern void Redraw();

extern char *text;
extern char *composition;
extern Sint32 cursor;
extern Sint32 selection_len;

int main(int argc, char **argv)
{
	SDL_bool done = SDL_FALSE;

	InitVideo();
	/* ... */

	SDL_StartTextInput();
	while (!done) {
		SDL_Event event;
		if (SDL_PollEvent(&event)) {
			switch (event.type) {
			case SDL_QUIT:
				/* Quit */
				done = SDL_TRUE;
				break;
			case SDL_TEXTINPUT:
				/* Add new text onto the end of our text */
				strcat(text, event.text.text);
				break;
			case SDL_TEXTEDITING:
				/*
				Update the composition text.
				Update the cursor position.
				Update the selection length (if any).
				*/
				composition = event.edit.text;
				cursor = event.edit.start;
				selection_len = event.edit.length;
				break;
			}
		}
		Redraw();
	}

	SDL_Quit();

	return 0;
}

I linked the sdl libraries and also included the headers but now I don’t know what am I doing wrong. It always gives me the ‘referenced in function SDL_MAIN’ errors in the line with the ‘extern’ parts.

Was I supposed to define those extern variables my self?

2

That code example isn’t complete. I think it’s expected you add the memory allocation for the text yourself. Here’s a more complete example.

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

#include <SDL.h>

typedef struct Text {
	char * string;
	size_t size;   /* Size of allocated memory. */
	size_t length; /* Length of the actual string. */
} Text;

static int GrowText(Text * text, size_t new_size)
{
	char * new_text;
	text->size += new_size;

	new_text = SDL_realloc(text->string, text->size);
	if (!new_text) {
		SDL_free(text->string);
		return 1;
	}

	text->string = new_text;
	return 0;
}

static int AppendText(Text * text, char * text_to_add)
{
	size_t tta_length = SDL_strlen(text_to_add);

	/* Check if the text (including the terminating zero) even fits into the allocated memory. */
	if (text->size - text->length < tta_length + 1) {
		/* It doesn't fit. We have to allocate more memory. */
		/* Let's give it some extra bytes in case it's a short text. */
		size_t new_size = tta_length < 512 ? 512 : tta_length;
		if (GrowText(text, new_size)) {
			SDL_Log("Out of memory\n");
			return 1;
		}
	}

	text->length = SDL_strlcat(text->string, text_to_add, text->size);

	return 0;
}

static void RemoveCharacter(Text * text)
{
	/* Removing multi-byte characters from the UTF-8 string. */
	while (text->length && text->string[text->length - 1] < -64) {
		text->length--;
	}
	if (text->length) {
		text->length--;
	}
	text->string[text->length] = 0;
}

int main(int argc, char *argv[])
{
	int run = 1;
	Text text = {NULL, 0, 0};
	SDL_Window * window;

	if (GrowText(&text, 16)) {
		SDL_Log("Out of memory\n");
		return 1;
	}

	if (SDL_Init(SDL_INIT_VIDEO | SDL_INIT_EVENTS) < 0 ) {
		return 1;
	}

	window = SDL_CreateWindow("TextInput", 50, 50, 50, 50, SDL_WINDOW_SHOWN);
	if (!window) {
		SDL_Quit();
		return 2;
	}

	while (run) {
		SDL_Event e;
		while (SDL_PollEvent(&e)) {
			if (e.type == SDL_QUIT) {
				run = 0;
			} else if (e.type == SDL_TEXTINPUT) {
				if (AppendText(&text, e.text.text)) {
					run = 0;
					break;
				}
				SDL_Log("%s", text.string);
			} else if (e.type == SDL_KEYDOWN) {
				if (e.key.keysym.sym == SDLK_ESCAPE) {
					run = 0;
				} else if (e.key.keysym.sym == SDLK_BACKSPACE) {
					if (text.length > 0) {
						RemoveCharacter(&text);
						SDL_Log("%s", text.string);
					}
				}
			} else if (e.type == SDL_KEYUP) {
				if (e.key.keysym.sym == SDLK_RETURN || e.key.keysym.sym == SDLK_KP_ENTER) {
					text.string[0] = 0;
					text.length = 0;
					SDL_Log("-----------");
				}
			}
		}

		SDL_Delay(1);
	}

	SDL_free(text.string);

	SDL_DestroyWindow(window);
	SDL_Quit();

	return 0;
}
3

Welp, I was expecting some textbox showing characters inputted by the user appearing, but anyways, thanks, it worked! :grin: