How to initialize nested array of structs in C++? - c++

Question

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 *"

Answer 1

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++.

Answer 2

In order to initialize your pointers, you have to create the pointed structures first, for example using new.
Notice that, if you want to treat Display_font.chars and Display_font_char.data as arrays, you should save their sizes (e.g. through a size_t data_size member).
In the example below I create the arrays with new[] and I delete them later on with delete[].
[Demo]
#include <iostream> // cout
#include <ostream>
struct Display_font_char
{
unsigned char* data;
size_t data_size;
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 = [";
for (size_t i{0}; i < f.data_size; ++i)
{
os << ((i == 0) ? "" : ", ") << static_cast<int>(f.data[i]);
}
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
{
Display_font_char* chars;
size_t chars_size;
unsigned char rangeStart;
unsigned char rangeEnd;
};
std::ostream& operator<<(std::ostream& os, const Display_font& f)
{
os << "chars = [\n";
for (size_t i{0}; i < f.chars_size; ++i)
{
os << ((i == 0) ? "" : ", ") << f.chars[i];
}
os << "]\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 = {
new Display_font_char[1]{
new unsigned char[4]{1, 2, 3},
3, // data size
1, 2,
3u, 4u, 5u
},
1, // chars size
1, 2
};
std::cout << font;
delete[] font.chars[0].data;
delete[] font.chars;
}
This other version uses std::vector instead of Display_font_char* and unsigned char*, so you don't have to do care about memory allocations/deallocations.
[Demo]
#include <iostream> // cout
#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::vector<Display_font_char> chars;
unsigned char rangeStart;
unsigned char rangeEnd;
};
std::ostream& operator<<(std::ostream& os, const Display_font& f)
{
os << "chars = [\n";
bool first{true};
for (auto& c : f.chars)
{
os << (first ? "" : ", ") << c;
first = false;
}
os << "]\n";
os << "trangeStart = " << static_cast<int>(f.rangeStart) << "\n";
os << "rangeEnd = " << static_cast<int>(f.rangeEnd) << "\n";
return os;
}
int main()
{
const Display_font font{
{ { {1, 2, 3}, 1, 2, 3u, 4u, 5u } },
1,
2
};
std::cout << font;
}