Missing Function Body or Variable
The latest version of this topic can be found at Missing Function Body or Variable.
With just a function prototype, the compiler can continue without error, but the linker cannot resolve a call to an address because there is no function code or variable space reserved. You will not see this error until you create a call to the function that the linker must resolve.
Example
The function call in main will cause LNK2019 because the prototype allows the compiler to think the function exists. The linker finds that it doesn't.
// LNK2019_MFBV.cpp
// LNK2019 expected
void DoSomething(void);
int main() {
DoSomething();
}
Example
In C++, make sure that you include the implementation of a specific function for a class and not just a prototype in the class definition. If you are defining the class outside of the header file, be sure to include the class name before the function (Classname``::``memberfunction).
// LNK2019_MFBV_2.cpp
// LNK2019 expected
struct A {
static void Test();
};
// Should be void A::Test() {}
void Test() {}
int main() {
A AObject;
AObject.Test();
}