CODEWITHSUNDEEP
c++parsing
user302099
user302099

Reputation: 635

Parsing C++ to make some changes in the code

I would like to write a small tool that takes a C++ program (a single .cpp file), finds the "main" function and adds 2 function calls to it, one in the beginning and one in the end.

How can this be done? Can I use g++'s parsing mechanism (or any other parser)?

Upvotes: 11

Views: 512

Answers (5)

Ira Baxter
Ira Baxter

Reputation: 95420

If you have control of your main program, you can hack a script to do this, and that's by far the easiet way. Simply make sure the insertion points are obvious (odd comments, required placement of tokens, you choose) and unique (including outlawing general coding practices if you have to, to ensure the uniqueness you need is real). Then a dumb string hacking tool to read the source, find the unique markers, and insert your desired calls will work fine.

If the souce of the main program comes from others sources, and you don't have control, then to do this well you need a full C++ program transformation engine. You don't want to build this yourself, as just the C++ parser is an enormous effort to get right. Others here have mentioned Clang and GCC as answers.

An alternative is our DMS Software Reengineering Toolkit with its C++ front end. DMS, using its C++ front end, can parse code (for a variety of C++ dialects), builds ASTs, carry out full name/type resolution to determine the meaning/definition/use of all symbols. It provides procedural and source-to-source transformations to enable changes to the AST, and can regenerate compilable source code complete with original comments.

Upvotes: 1

shoosh
shoosh

Reputation: 79011

Adding a function at the beginning of main() and at the end of main() is a bad idea. What if someone calls return in the middle?.
A better idea is to instantiate a class at the beginning of main() and let that class destructor do the call function you want called at the end. This would ensure that that function always get called.

Upvotes: 2

Lambdageek
Lambdageek

Reputation: 12475

As suggested by some commenters, let me put forward my idea as an answer:

So basically, the idea is: 

... original .cpp file ...

#include <yourHeader>
namespace { 
  SpecialClass  specialClassInstance;
}

Where SpecialClass is something like:

class SpecialClass {
  public:
    SpecialClass() {
        firstFunction();
    }

    ~SpecialClass() {
        secondFunction();
    }
}

This way, you don't need to parse the C++ file. Since you are declaring a global, its constructor will run before main starts and its destructor will run after main returns.

The downside is that you don't get to know the relative order of when your global is constructed compared to others. So if you need to guarantee that firstFunction is called before any other constructor elsewhere in the entire program, you're out of luck.

Upvotes: 6

Barry Wark
Barry Wark

Reputation: 107764

I've heard the GCC parser is both hard to use and even harder to get at without invoking the whole toolchain. I would try the clang C/C++ parser (libparse), and the tutorials linked in this question.

Upvotes: 2

Johannes Schaub - litb
Johannes Schaub - litb

Reputation: 507283

If you want to make it solid, use clang's libraries.

Upvotes: 8

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