Thread: Strange behaviour increasing this.cur_size?

Can't figure out why this.cur_size never increases above 1 when i add characters to this.char. Any ideas whats wrong with the appendInTextBox?

Code:

/**     \ TEXT BOX /



    typedef struct TextBox {
        SDL_Texture* texture_normal;
        SDL_Texture* texture_selected;
        SDL_Texture* texture_btn_txt;
        SDL_Rect rect_box;
        SDL_Rect rect_text;
        int cur_size;
        int max_size;
        char* msg;
        bool highlighted;
        bool selected;
        bool show;
    } TextBox;


*/


TextBox createTextBox(SDL_Texture* tex_norm, SDL_Texture* tex_select, TTF_Font *font, SDL_Color txt_color, int x, int y, bool show)
{
    TextBox this;
    this.rect_box.x = x;
    this.rect_box.y = y;
    if (tex_norm != NULL) {
        this.texture_normal = tex_norm;
        SDL_QueryTexture(this.texture_normal, NULL, NULL, &this.rect_box.w, &this.rect_box.h);
    }
    if (tex_select != NULL) {
        this.texture_selected = tex_select;
    }
    this.highlighted = false;
    this.selected = false;
    this.show = show;
    this.max_size = 10;
    this.cur_size = 0;
    this.msg = malloc(this.max_size + 2);
    this.msg[0] = '\0';
    return this;
}


void appendInTextBox(TextBox this, char* msg_)
{
    for (int i = 0; msg_[i] != '\0'; i++)
    {
        if (this.cur_size < this.max_size) {
            this.msg[this.cur_size] = msg_[i];
            this.cur_size++;
            this.msg[this.cur_size] = '\0';
        }
    }
    printf("cur: %d, s: %s\n", this.cur_size, this.msg);
}

The problem is that you are passing a copy of the TextBox struct data into appendInTextBox, then modifying that copy, then basicaly throwing it away. The usual way to do this is to pass in a pointer. And you don't need the trailing underscore in the msg parameter.

Code:

void appendInTextBox(TextBox *this, char *msg) {
    for (int i = 0; msg[i] && this->cur_size < this->max_size; i++)
        this->msg[this->cur_size++] = msg[i];
    this->msg[this->cur_size] = '\0';
    printf("cur: %d, s: %s\n", this->cur_size, this->msg);
}