static map initialization error - unresolved external symbol

Question

Using Visual Studio 2015, I have been trying load a table that contains floating point values for degrees converted to radians. Since the MathFunctions class is static (static functions), I am trying to initialize the map that withholds the converted radian values. But I keep getting LNK2001 unresolved symbol error when I reference the map inside the InitTables/Degree2Radians functions - Note that both the header and cpp files lie in the same project under the same folder "Utilities"

Declarations (MathFunctions.h)

 #pragma once
 #ifndef MATHFUNCTIONS_H
 #define MATHFUNCTIONS_H
 #define _USE_MATH_DEFINES
 #include <math.h>
 #include <map>
 #include <fstream>
 using namespace std;

namespace LookupTables
{
    class MathFunctions
    {
      private:
        static map<short, float>Degree2RadiansTable;

      public:
        static void InitTables();
        static float Degree2Radians(short angleInDegrees);      
};
}
#endif

While Definitions (MathFunctions.cpp) are as follows

namespace LookupTables
{
    void MathFunctions::InitTables()
    {
        // Load degree2radians table
        short degrees = 0;
        float radians = 0;
        ifstream infile("..\Tables\Degree2Radians.txt");
        if (infile.good() && infile.is_open())
        {
                while (infile >> degrees && infile >>radians) 
                {
                    MathFunctions::Degree2RadiansTable.insert({ degrees,radians });
                }
        }
        infile.close();     
    }

    float MathFunctions::Degree2Radians(short angleInDegrees)
    {
        return MathFunctions::Degree2RadiansTable[angleInDegrees];
    }
}

I am not sure what is wrong.

Are you linking with the place that defines `Degree2Radians()`? — bobah, Aug 31 '15 at 07:13
@bobah - Linking? They are under the same folder and project. Not external. — Wajih, Aug 31 '15 at 07:16
you need to construct it somewhere : `static map MathFunctions::Degree2RadiansTable;` — UmNyobe, Aug 31 '15 at 07:18
@UmNyobe - You mean at the top of the cpp file after header include directives? — Wajih, Aug 31 '15 at 07:20
Say this in the `.cpp`: `map MathFunctions::Degree2RadiansTable;` — bobah, Aug 31 '15 at 07:21
@bobah - Well I compiled now as per UmNyobe and bobah - But I dont see the purpose of a declaration in header file. Anyway, thanks — Wajih, Aug 31 '15 at 07:23
@UmNyobe - Put your answer and I will mark it. You came up first with the answer. — Wajih, Aug 31 '15 at 07:24
Declarations are there to let client code correctly refer to the externally _defined_ symbol — bobah, Aug 31 '15 at 07:24
@UmNyobe - `static` keyword should not be used in definition (it means different things in that context. — bobah, Aug 31 '15 at 07:25
Am sorry. my bad - It is not compiling. My apologies, the error is still there — Wajih, Aug 31 '15 at 07:27
Dont know if this is a compiler bug, but I tried to construct in the cpp file with and without the static keyword map Degree2RadiansTable; and static map Degree2RadiansTable; No luck — Wajih, Aug 31 '15 at 07:28
Compiler bug? Of course not. It's your lack of knowledge of C++. Like this `map MathFunctions::Degree2RadiansTable;`. No static but don't forget the class name. — john, Aug 31 '15 at 07:30
Sorry if the above seems rude, but it gets me when beginners say 'compiler bug'. — john, Aug 31 '15 at 07:32
@john - ? Well ok not a compiler bug, but still not compiling. — Wajih, Aug 31 '15 at 07:32
Well then you've made some other mistake. Please post exactly what you are trying to compile. — john, Aug 31 '15 at 07:33
@john - Posted the whole code. This is a simple class, nothing fancy here. — Wajih, Aug 31 '15 at 07:39
@john - Bingo! map MathFunctions::Degree2RadiansTable; was the answer — Wajih, Aug 31 '15 at 07:43

static map initialization error - unresolved external symbol

0 Answers0