Build AST from C code

Question

How can I build an AST (Abstract Syntax Tree) from gcc C code in order to make some modifications, like converting some int variables to float, and reproduce(generate) the c

Answer 1

What you are asking for is a C source-to-source transformer. Such a tool is very difficult to build, partly because of the inherent complexity of C, and partly because of the C preprocessor: the AST may contain fragments from system headers etc. that you need to handle properly while unparsing (emitting C code again at the end).

You could give Robert Grimm's SuperC a try: https://cs.nyu.edu/rgrimm/xtc/ That particular parser is supposed to handle all of C (including the preprocessor bits). I don't know if it can handle unparsing, but that should be comparatively easy (read: still lots of work) to do.