I have the following definitions:

struct Display_font_char 
{
    unsigned char * data;
    int originX;
    int originY;
    unsigned int width;
    unsigned int height;
    unsigned int delta;
};

struct Display_font 
{
    Display_font_char * chars;
    unsigned char rangeStart;
    unsigned char rangeEnd;
};

How can I initialize it inplace? I'm trying:

const Display_font font = 
{
    {
        {
            { 1, 2, 3 },
            1,
            2,
            3u,
            4u,
            5u
        }
    },
    1u,
    2u
}

However, I'm getting an error: "Cannot use value of type int to initialize field of type Display_font_char *"

CodePudding user response：

You cannot initialise a pointer with a braced init list of multiple values.

Here is an example of how you could initialise an instance of the class:

unsigned char uc[] = { 1, 2, 3 };
Display_font_char fc {
    uc,
    1,
    2,
    3u,
    4u,
    5u,
};
const Display_font font = 
{
    &fc,
    1u,
    2u,
};

As a sidenote, if you were to switch to C, then you could use compound literals:

const struct Display_font font = 
{
    &(struct Display_font_char){
        (unsigned char []){ 1, 2, 3 },
        1,
        2,
        3u,
        4u,
        5u
    },
    1u,
    2u
};

But alas, compound literals don't exist in C .

CodePudding user response：

In order to initialize your pointers, you have to create the pointed structures first, for example using new.

Notice that, if you want to keep an unsigned char* array in Display_font_char, you should need to know its size (e.g. through a size_t data_size member).

In the example below I create the structs with new and I use data as an array of chars, so I can easily print it.

[Demo]

#include <iostream>  // cout
#include <ostream>
#include <vector>

struct Display_font_char 
{
    unsigned char* data;
    int originX;
    int originY;
    unsigned int width;
    unsigned int height;
    unsigned int delta;
};
std::ostream& operator<<(std::ostream& os, const Display_font_char& f)
{
    os << "\tdata = " << f.data << "\n";
    os << "\toriginX = " << f.originX << "\n";
    os << "\toriginY = " << f.originY << "\n";
    os << "\twidth = " << f.width << "\n";
    os << "\theight = " << f.height << "\n";
    os << "\tdelta = " << f.delta << "\n";
    return os;
}

struct Display_font 
{
    Display_font_char* chars;
    unsigned char rangeStart;
    unsigned char rangeEnd;
};
std::ostream& operator<<(std::ostream& os, const Display_font& f)
{
    os << "chars =\n" << *f.chars << "\n";
    os << "rangeStart = " << f.rangeStart << "\n";
    os << "rangeEnd = " << f.rangeEnd << "\n";
    return os;
}

int main()
{
    const Display_font font = {
        new Display_font_char{new unsigned char[4]{'1', '2', '3', 0}, 1, 2, 3u, 4u, 5u},
        '1',
        '2'
    };
    std::cout << font;
}

This other version uses:

• std::vector instead of unsigned char*, and
• std::unique_ptr<Display_font_char> instead of Display_font_char*.

So you don't have to do care about memory allocations/deallocations.

[Demo]

#include <iostream>  // cout
#include <memory>  // make_unique, unique_ptr
#include <ostream>
#include <vector>

struct Display_font_char
{
    std::vector<unsigned char> data;
    int originX;
    int originY;
    unsigned int width;
    unsigned int height;
    unsigned int delta;
};
std::ostream& operator<<(std::ostream& os, const Display_font_char& f)
{
    os << "\tdata = [";
    bool first{true};
    for (auto& d : f.data)
    {
        os << (first ? "" : ", ") << static_cast<int>(d);
        first = false;
    }
    os << "]\n";
    os << "\toriginX = " << f.originX << "\n";
    os << "\toriginY = " << f.originY << "\n";
    os << "\twidth = " << f.width << "\n";
    os << "\theight = " << f.height << "\n";
    os << "\tdelta = " << f.delta << "\n";
    return os;
}

struct Display_font 
{
    std::unique_ptr<Display_font_char> chars;
    unsigned char rangeStart;
    unsigned char rangeEnd;

};
std::ostream& operator<<(std::ostream& os, const Display_font& f)
{
    os << "chars =\n" << *(f.chars.get()) << "\n";
    os << "rangeStart = " << static_cast<int>(f.rangeStart) << "\n";
    os << "rangeEnd = " << static_cast<int>(f.rangeEnd) << "\n";
    return os;
}

int main()
{
    const Display_font font{
        std::make_unique<Display_font_char>(
            std::vector<unsigned char>{1, 2, 3}, 1, 2, 3u, 4u, 5u),
        1,
        2
    };
    std::cout << font;
}