CODEWITHSUNDEEP
c++
Maik Klein
Maik Klein

Reputation: 16148

How do I prevent a source file from depending on an include inside a header file?

//Foo.h
#include <string>
struct Foo;

//main.cpp
#include "Foo.h"
int main(int argc, char *argv[])
{
  std::string s = "hello";
}

The problem I have with this code is that #include <string> leaks into main.cpp. #include <string> is needed in main.cpp to compile but if in a future version Foo.h doesn't need string anymore, main.cpp will not compile.

Is there a way to prevent this?

Edit: I know that I can manage this on my own by always including every file that I need but I am working in a team and everyone does their own thing and it is a complete mess. So I was wondering if there is a way to force this.

Comments seem to indicate that we have to manage it manually. I guess this answers my question.

Upvotes: 2

Views: 870

Answers (2)

MinusBrain
MinusBrain

Reputation: 96

Let every file include only the dependencies it really needs. Also you should protect your own header files using include guards (C++ #include guards).

Foo.h:

#ifndef _INCLUDED_FOO_H_
#define _INCLUDED_FOO_H_ 

// Only #include <string> here if it is needed in the Foo.h
// ...
struct Foo;
// ...

#endif

main.cpp:

#include <string>
#include "Foo.h"
int main(int argc, char *argv[])
{
   std::string s = "hello";
}

This way main.cpp does still compile even if Foo.h changes later.

Upvotes: 2

Rob Kennedy
Rob Kennedy

Reputation: 163287

No, there is no automated way to protect yourself from inadvertently relying on headers that you've included through other headers.

What you need to do is discipline yourself to include the relevant headers in each source file that uses them, even if each #include directive isn't strictly required in each source file.

The consequences of forgetting that aren't dire, though. If Foo.h eventually changes to no longer include string, then the code will fail to compile, but the fix is easy and takes almost no time. It's not worth worrying about.

Upvotes: 4

Related Questions