Union of same type in C++

user_368599 0
Viewed 2484

Whenever I see examples of union, they are always different types. For example, from MSDN:

// declaring_a_union.cpp
union DATATYPE    // Declare union type
{
    char   ch;
    int    i;
    long   l;
    float  f;
    double d;
} var1;          // Optional declaration of union variable

int main()
{
}

What happens if I have a union (in this case anonymous, but that shouldn't matter) like this:

union
{
    float m_1stVar;
    float m_1stVarAlternateName;
};

Regardless of whether this is good practice or not, will this cause any issues?

unions c++
3 Answers

This is legal and very useful in situations where you have different contexts, where different names would be more appropriate. Take a four member vector vec4 type for example (similar to what you'd find in GLSL):

vec4 v(1., 1., 1., 1.);

// 1. Access as spatial coordinates
v.x;
v.y;
v.z;
v.w;

// 2. Access as color coordinates (red, green, blue, alpha)
v.r;
v.g;
v.b; 
v.a;

// 3 Access as texture coordinates
v.s;
v.t;
v.p;
v.q;

A vec4 may only have four members of the same type, but you'd use different names to refer to the same objects, depending on the context.

user_42245750

An issue would arise only if you want to have unique values for the two variables. In your use-case, it should work fine.

user_99771740
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