I'd like to package a library I'm working on as a header-only library to make it easier for clients to use. (It's small and there's really no reason to put it into a separate translation unit开发者_开发知识库) However, I cannot simply put my code in headers because this violates C++'s one definition rule. (Assuming that the library header is included in multiple translation units of a client project)
How does one modify a library to make it header-only?
You can use the inline
keyword:
// header.hpp (included into multiple translation units)
void foo_bad() {} // multiple definitions, one in every translation unit :(
inline void foo_good() {} // ok :)
inline
allows the linker to simply pick one definition and discard the rest.
(As such, if those definitions don't actually match, you get a good dose of undefined behavior...!)
As an aside, member functions defined within a class-type, are implicitly marked inline
:
struct myclass
{
void i_am_inline_implicitly()
{
// because my definition is here
}
void but_i_am_not();
void neither_am_i();
};
inline void myclass::but_i_am_not()
{
// but that doesn't mean my definition cannot be explicitly inline
}
void myclass::neither_am_i()
{
// but in this case, no inline for me :(
}
Use header guards as Liz suggests and don't forget to put "inline" before your function methods.
ie
#ifndef MY_HEADER_H_
#define MY_HEADER_H_
inline RetType FunctionName( ParamType1 param1, ParamType2 param2 )
{
// Function body
return retType;
}
#endif
Also, I think you'll need to avoid any use of global variables or static variables in your header-only-library code.
Use header guards for the parts that compile in one place.
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