Game Engine Architecture

3.2. Data, Code, and Memory in C/C++ 109

Unresolved Reference???

???

Multiply-Defined Symbol

???

foo.cpp

U32 gGlobalA ;

U32 gGlobalB ;

void f ()

{

// ...

gGlobalC = 5.3f;

gGlobalD = -2;

// ...}

extern U 32 gGlobalC ;

bar.cpp

F32 gGlobalC ;

void g ()

{

// ... U32 a = gGlobalA ;

// ...

f();

// ...

gGlobalB = 0;

}

extern U 32 gGlobalA ;

extern U 32 gGlobalB ;

extern void f ();

spam.cpp

U32 gGlobalA ;

void h()

{

// ...

}

Figure 3.9. The two most common linker errors.

foo.cpp

U32 gGlobalA ;

U32 gGlobalB ;

void f()

{

// ...

gGlobalC = 5.3f;

// ...}

extern U 32 gGlobalC ;

bar.cpp

F32 gGlobalC ;

void g ()

{

// ...

U32 a = gGlobalA ;

// ... f();

// ...

gGlobalB = 0;

}

extern U 32 gGlobalA ;

extern U 32 gGlobalB ;

extern void f ();

Figure 3.7. Unresolved external references in two translation units.

foo.cpp

U32 gGlobalA ;

U32 gGlobalB ;

void f ()

{

// ...

gGlobalC = 5.3f;

// ...}

extern U 32 gGlobalC ;

bar.cpp

F32 gGlobalC ;

void g()

{

// ...

U32 a = gGlobalA ;

// ... f();

// ...

gGlobalB = 0;

}

extern U 32 gGlobalA ;

extern U 32 gGlobalB ;

extern void f ();

Figure 3.8. Fully resolved external references after successful linking.