This piece of code:

#include 
#include 

#include 
#include 
#include 
#include 

int main() {
    
    SDL_Init(SDL_INIT_VIDEO);
    TTF_Init();
    
    char* mem = nullptr;
    size_t size = 0;
    {
        std::ifstream font_load{"test_font.ttf", std::ios_base::in | std::ios_base::binary};
        font_load.seekg(0, std::ios_base::end);
        size = font_load.tellg();
        font_load.seekg(0);
        mem = new char[size];
        font_load.read(mem, size);
    }
    SDL_IOStream* io = SDL_IOFromConstMem(mem, size);
    TTF_Font* f = TTF_OpenFontIO(io, true, 24.0f);
    delete mem;
    if( f == nullptr ) {
        std::cout << "Font load error: " << SDL_GetError() << std::endl;
    } else {
        SDL_Color f_color{255,255,255,255};
        std::string test_text{ "Example text" };
        SDL_Surface* surf = TTF_RenderText_Blended(
            f,
            test_text.c_str(),
            test_text.size(),
            f_color
        );
        if( surf == nullptr ) {
            std::cout << "Surface creation error: " << SDL_GetError() << std::endl;
        } else {
            std::cout << "Surface created!" << std::endl;
            SDL_DestroySurface( surf );
        }
        TTF_CloseFont( f );
    }
    
    TTF_Quit();
    SDL_Quit();
    
    return 0;
}

...after compiling under MSVC on Windows prints:

Surface creation error: Text has zero width

What may be the cause of "text has zero width" error? I tried also loading font directly with TTF_Font* f = TTF_OpenFont("test_font.ttf", 24.0f); which works. However in my production code sometimes I have to load font thru SDL's IO.