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.NET Forum / Languages / Managed C++ / September 2007"union" syntax
Hi all, I'm struggling to do something really basic. How do I declare a structure that has a union that maps an array of 3 chars with 3 distinct char variables. In other words, I want the following two statements to put the same value into the same byte in the structure: myStruct.Vars[1] = 5; myStruct.Var1 = 5; TIA - Bob How about just including this somewhere: #define myStruct.Var1 myStruct.Var[1] To be honest, not sure if the above works, and it is a purely syntactical solution, and may not address the reasons WHY you want this capability. [==Peter==] > Hi all, > [quoted text clipped - 7 lines] > > TIA - Bob Well, that's certainly thinking outside of the box. But I'd be surprised if it compiles. As for why I want this: I have a structure that is used to pass data into my public API: struct MyStates { BOOL X_Axis_Enabled; BOOL Y_Axis_Enabled; BOOL Z_Axis_Enabled; } Now, I've decided that it would be very convenient for me to be able to access the members of this structure as though they were members of an array, like this: struct MyStates { BOOL Enabled[3]; } But I can't change the structure in a way that will break existing code that accesses the individual member variables. - Bob > How about just including this somewhere: > [quoted text clipped - 4 lines] > > [==Peter==] > Well, that's certainly thinking outside of the box. But I'd be surprised if > it compiles. [quoted text clipped - 18 lines] > But I can't change the structure in a way that will break existing code that > accesses the individual member variables. Bob: How about struct MyStates { BOOL X_Axis_Enabled; BOOL Y_Axis_Enabled; BOOL Z_Axis_Enabled; BOOL& operator[](int i) { BOOL* enabled[3]; enabled[0] = &X_Axis_Enabled; enabled[1] = &Y_Axis_Enabled; enabled[2] = &Z_Axis_Enabled; return *(enabled[i]); } }; int main() { MyStates myStates; myStates[0] = TRUE; myStates[1] = FALSE; myStates[2] = TRUE; return 0; }  SignatureDavid Wilkinson Visual C++ MVP >How about just including this somewhere: > >#define myStruct.Var1 myStruct.Var[1] > >To be honest, not sure if the above works It does not. You can't define a macro name that contains a dot. SignatureDoug Harrison Visual C++ MVP >Hi all, > [quoted text clipped - 5 lines] > myStruct.Vars[1] = 5; > myStruct.Var1 = 5; You could do it with: union U { struct { char Var0; char Var1; char Var2; }; char Vars[3]; }; This makes use of an anonymous struct, which is a VC extension, so it's not going to be portable. SignatureDoug Harrison Visual C++ MVP Thanks Doug, that's just what I was looking for. - Bob >>Hi all, >> [quoted text clipped - 22 lines] > not > going to be portable. Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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