Initialize std::vector in a struct

user_382485 0
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I have a struct with 2 std::vectors as given below. I want to initialize the vector with 2048 elements having initial value 0.0.

struct PixelMaps
{
    vector<double> pixelMapX;
    vector<double> pixelMapY;
};

I tried the following code. This creates the vector of 2 elements only. How can I initialize the structure with 2048 elements in a single statement with initialization list?

PixelMaps test{ {2048,0.0}, {2048, 0.0} };
c++17 c++
2 Answers

std::vector has a constructor using std::initializer_list, so you can't use brace-init-list - it will always end up in that constructor. You need more explicit initialization:

PixelMaps test{ std::vector(2048,0.0), std::vector(2048, 0.0) };

Or (pre C++17)

PixelMaps test{ std::vector<double>(2048,0.0), std::vector<double>(2048, 0.0) };
user_79768050

Depending on your C++ taste, in C++20 you could write

#include <vector>

struct PixelMaps
{
    std::vector<double> pixelMapX;
    std::vector<double> pixelMapY;
};

int main() 
{ 
    
    PixelMaps test {
        .pixelMapX {std::vector(2048,0.0)},
        .pixelMapY {std::vector(2048,0.0)}
    };
}

This is known as designated initialization.

user_65306950
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