SDL text box highlighting text - c++

Question

I am making a program in C++ that uses SDL to display text boxes. I've made the basic functions of my text boxes like typing text, limitations, copy/paste, etc. but I am stuck at make it able to highlight text.
Here's how I draw textboxes:
void draw_text_box(SDL_Surface *screan, char *message, struct textbox *text_box, int r, int g, int b)
{
int temp_width;
int temp_frame;
SDL_Surface *text;
SDL_Color textcolor = {0,0,0,0};
SDL_Rect temp_location, clr_box;
temp_width = text_box->location.w; //preserve the correct width
temp_location = text_box->location;
temp_location.y += 4;
temp_location.h = 12;
clr_box = text_box->location;
//colors!
textcolor.r = r;
textcolor.g = g;
textcolor.b = b;
//text = TTF_RenderText_Solid(ttf_font, text_box->prev_message, textcolor);
//SDL_BlitSurface( text, NULL, screan, &text_box->location);//<-changes "location" width to width of text
//clear
SDL_FillRect(screan, &clr_box, SDL_MapRGB(screen->format, 0, 0, 0));
//strcpy(text_box->prev_message, message);
//set the text
text = TTF_RenderText_Solid(ttf_font, message, textcolor);
if(!text) return;
//set the offset
temp_location.x = text_box->last_shift;
temp_location.y = 0;
temp_location.h = text->h;
if(text_box->cursor_loc - text_box->last_shift > temp_location.w)
temp_location.x = text_box->cursor_loc - temp_location.w;
if(text_box->cursor_loc - 3 < text_box->last_shift)
temp_location.x = text_box->cursor_loc - 3;
if(temp_location.x < 0) temp_location.x = 0;
text_box->last_shift = temp_location.x;
//draw
SDL_BlitSurface( text, &temp_location, screan, &text_box->location);//<-changes "location" width to width of text
text_box->location.w = temp_width;
}
Setting the text:
void set_text_box_text(SDL_Surface *screan, struct textbox *text_box, char *message)
{
if(text_box->message != message)
strcpy(text_box->message, message);
text_box->char_amt = strlen(message);
text_box->cursor = text_box->char_amt;
text_box->last_shift = 0;
if (screan) //if not NULL
{
if (text_box->selected)
select_text_box(screan,text_box);
else
unselect_text_box(screan,text_box);
}
else
{
;//text_box->prev_message[0] = '\0';
}
}
Select and deselect the textbox:
void select_text_box(SDL_Surface *screan, struct textbox *text_box)
{
char temp_message[405] = "";
char temp_left[405];
int i;
text_box->selected = 1;
if (text_box->pass_char == '\0')
{
if (text_box->cursor != 0)
{
left(temp_left, text_box->message, text_box->cursor);
strcat(temp_message, temp_left);
}
temp_message[text_box->cursor] = '|';
temp_message[text_box->cursor + 1] = '\0';
right(temp_left, text_box->message, text_box->cursor);
strcat(temp_message, temp_left);
}
else
{
for(i=0;i<text_box->cursor;i++)
temp_message[i] = text_box->pass_char;
temp_message[i] = '|';
for(i++;i<text_box->char_amt + 1;i++)
temp_message[i] = text_box->pass_char;
temp_message[i] = '\0';
}
draw_text_box(screan, temp_message, text_box, 250, 250, 250);
}
void unselect_text_box(SDL_Surface *screan, struct textbox *text_box)
{
char temp_message[405];
int i;
text_box->selected = 0;
if (text_box->pass_char == '\0')
draw_text_box(screan, text_box->message, text_box, 250, 250, 250);
else
{
for(i=0;i<text_box->char_amt;i++)
temp_message[i] = text_box->pass_char;
temp_message[i] = '\0';
draw_text_box(screan, temp_message, text_box, 250, 250, 250);
}
}