Appeal to fields of an array of objects

Question

I decided to make my own simple game. For "procedural texture drawing" I wanted to create color matrices and fill them, tried to do it directly:

struct blockColor{ int r; int g; int b; blockColor() { r = 0; g = 0; b = 0; }; }; blockColor brickColorMap[8][8]; brickColorMap[8][8].r = { {54, 54, 54, 54, 64, 54, 54, 54}, {54, 54, 54, 54, 64, 54, 54, 54}, {64, 64, 64, 64, 64, 64, 64, 64}, {54, 64, 54, 54, 54, 54, 64, 54}, {54, 64, 54, 54, 54, 54, 64, 54}, {64, 64, 64, 64, 64, 64, 64, 64}, {54, 54, 54, 64, 54, 54, 54, 54}, {54, 54, 54, 64, 54, 54, 54, 54} };

The compiler, of course, gives an error. How would it be correct to fill in such a matrix of fields?

Nikolay Nikolay 286 one ten · Accepted Answer · 2015-06-05T14:29:17

I would suggest just making the initialization function. Those. initialize the matrix at the start of the program from another array. Something like this:

 struct blockColor{ int r; int g; int b; blockColor() { r = 0; g = 0; b = 0; }; }; blockColor brickColorMap[8][8]; int r_color[8][8] = { { 54, 54, 54, 54, 64, 54, 54, 54 }, { 54, 54, 54, 54, 64, 54, 54, 54 }, { 64, 64, 64, 64, 64, 64, 64, 64 }, { 54, 64, 54, 54, 54, 54, 64, 54 }, { 54, 64, 54, 54, 54, 54, 64, 54 }, { 64, 64, 64, 64, 64, 64, 64, 64 }, { 54, 54, 54, 64, 54, 54, 54, 54 }, { 54, 54, 54, 64, 54, 54, 54, 54 } }; int g_color[8][8] = { // ... }; int b_color[8][8] = { // ... }; void initColor(int blockColor::*member, int data[8][8]) { for (int i = 0; i < 8; ++i) for (int j = 0; j < 8; ++j) brickColorMap[i][j].*member = data[i][j]; } int main(int argc, char** argv) { initColor(&blockColor::r, r_color); initColor(&blockColor::g, g_color); initColor(&blockColor::b, b_color); return 0; }

A pointer to a member of the structure is used as a parameter so that one initColor function can be reused for all 3 colors.

Answer 2 · 2015-06-05T12:13:52

In C ++ 11, initializer_list appeared. You can do this:

 #include <initializer_list> struct blockColor{ int r; int g; int b; blockColor() { r = 0; g = 0; b = 0; }; blockColor(std::initializer_list<int> init) { const int* it = init.begin(); r = *it++; g = *it++; b = *it; }; }; blockColor brickColorMap[3][2] = { { { 54, 54, 54 }, { 54, 54, 54 } }, { { 64, 64, 64 }, { 64, 64, 64 } }, { { 54, 64, 54 }, { 54, 54, 54 } } };

That is, in this way it is possible to specify all three fields at once in one two-dimensional array (r, g, b) instead of creating three matrices for each color separately?
I tried your code - it is not compiled - "Initialization of blockColor type objects using the expression {....} is not allowed. I work in MVS2010
What is the initializer_list here for, it is completely for other purposes ...
Um .. And why initializer list, if the assignment of structures across the fields has been working since ancient times?
The option proposed by @Qwertiy is really better and works in VS2010.

Qwertiy ♦ Qwertiy 76.2k 17 73 200 · Answer 3 · 2015-06-05T15:10:46

http://codepad.org/9Uxqmnn3

 struct blockColor { int r, g, b; }; blockColor brickColorMap[3][2] = { { { 54, 54, 54 }, { 54, 54, 54 } }, { { 64, 64, 64 }, { 64, 64, 64 } }, { { 54, 64, 54 }, { 54, 54, 54 } } };

Answer 4 · 2015-06-05T14:46:34

You just need to add a constructor for all 3 colors and use it:

 struct blockColor{ int r; int g; int b; blockColor() { r = 0; g = 0; b = 0; } blockColor(int r, int g, int b) { this->r = r; this->g = g; this->b = b; } }; blockColor brickColorMap[2][2] = { {blockColor(54, 54, 54), blockColor(55, 55, 55)}, {blockColor(56, 56, 56), blockColor(57, 57, 57)}, };

Initialization in the style of modern C ++, which MSVC2010 does not fully support (in particular, such initialization will not work there):

 blockColor brickColorMap[2][2] = { {{54, 54, 54}, {55, 55, 55}}, {{56, 56, 56}, {57, 57, 57}}, };

At least, g ++ spits in the case of the present constructor.
If you remove constructors, aggregation initialization will occur, which does not use a constructor.
This is quite a method, I just don’t welcome aggregation initialization.
With the constructor, it does not compile: codepad.org/9Uxqmnn3 and codepad.org/sPoMOYN4
@Qwertiy, I don’t know what the compiler is and the flags on this codepad, here’s your ideone
There precisely there is an interpretation of warnings as errors.

Appeal to fields of an array of objects

4 answers 4

More articles: