Undefined reference to a function

[jarvis402]

I am learning stm32f407ve, And I am facing problem in building the project.

GPIO_Init( ) and GPIO_ReadFromInputPin( ) both functions are defined in the same files and declared in same files but when i build the project . I get Error for GPIO_ReadFromInputPin( ) and not for GPIO_Init( ) , how is this possible ?

[Tesla DeLorean · Accepted solution]

Missing some source code somewhere. 

Include files define interfaces and macros, they typically don't provide the code the Linker needs for closure. 

What library is this. Lacking broader context.