How to extract a single function from a source file

Question

I'm working on a small academic research about extremely long and complicated functions in the Linux kernel. I'm trying to figure out if there is a good reason to write 600 or 800 lines-long functions.

For that purpose, I would like to find a tool that can extract a function from a .c file, so I can run some automated tests on the function.

For example, If I have the function cifs_parse_mount_options() within the file connect.c, I'm seeking a solution that would roughly work like:

extract /fs/cifs/connect.c cifs_parse_mount_options

and return the 523 lines of code(!) of the function, from the opening braces to the closing braces.

Of course, any way of manipulating existing software packages like gcc to do that, would be most helpful too.

Thanks,

Udi

EDIT : The answers to Regex to pull out C function prototype declarations? convinced me that matching function declaration by regex is far from trivial.

Answer 1

Why don't you write a small PERL/PHP/Python script or even a small C++,Java or C# program that does that?

I don't know of any already-made tools to do that but writing the code to parse out the text file and extract a function body from a C++ code file should not take more than 20 lines of code.. The only difficult part will be locating the beginning of the function and that should be a relatively simple task using RegEx. After that, all you need is to iterate through the rest of the file keeping track of opening and closing curly braces and when you reach the function body closing brace you're done.

Answer 2

indent -kr code -o code.out

awk -f split.awk code.out

you have to adapt a little bit split.awk wich is somewhat specific to my code and refactoring needs (for example y have so struct who are not typedefs

And I'm sure you can make a nicer script :-)

--
BEGIN   { line=0; FS="";
    out=ARGV[ARGC-1]  ".out";
    var=ARGV[ARGC-1]  ".var";
    ext=ARGV[ARGC-1]  ".ext";
    def=ARGV[ARGC-1]  ".def";
    inc=ARGV[ARGC-1]  ".inc";
    typ=ARGV[ARGC-1]  ".typ";
    system ( rm " " -f " " out " " var " " ext " " def " " inc " " typ );
    }
/^[     ]*\/\/.*/   { print "comment :" $0 "\n"; print $0 >> out ; next ;}
/^#define.*/        { print "define :" $0 ; print $0 >>def ; next;}
/^#include.*/       { print "define :" $0 ; print $0 >>inc ; next;}
/^typedef.*{$/      { print "typedef var :" $0 "\n"; decl="typedef";print $0 >> typ;infile="typ";next;}
/^extern.*$/        { print "extern :" $0 "\n"; print $0 >> ext;infile="ext";next;}
/^[^    }].*{$/     { print "init var :" $0 "\n";decl="var";print $0 >> var; infile="vars";
                print $0;
                fout=gensub("^([^    \\*])*[    ]*([a-zA-A0-9_]*)\\[.*","\\2","g") ".vars";
                     print "var decl : " $0 "in file " fout;
                     print $0 >fout;
                next;
                        }
/^[^    }].*)$/     { print "func  :" $0 "\n";decl="func"; infile="func";
                print $0;
                fout=gensub("^.*[    \\*]([a-zA-A0-9_]*)[   ]*\\(.*","\\1","g") ".func";
                     print "function : " $0 "in file " fout;
                     print $0 >fout;
                next;
            }
/^}[    ]*$/        { print "end of " decl ":" $0 "\n"; 
                if(infile=="typ") {
                    print $0 >> typ;
                }else if (infile=="ext"){
                    print $0 >> ext;
                }else if (infile=="var") {
                    print $0 >> var;
                }else if ((infile=="func")||(infile=="vars")) {
                    print $0 >> fout; 
                    fflush (fout);
                    close (fout);
                }else if (infile=="def") {
                    print $0 >> def;
                }else if (infile=="inc"){
                    print $0 >> inc;
                }else print $0 >> out;
                next;
            }
/^[a-zA-Z_]/        { print "extern :" $0 "\n"; print $0 >> var;infile="var";next;}
            { print "other :" $0 "\n" ; 
                if(infile=="typ") {
                    print $0 >> typ;
                }else if (infile=="ext"){
                    print $0 >> ext;
                }else if (infile=="var") {
                    print $0 >> var;
                }else if ((infile=="func")||(infile=="vars")){
                    print $0 >> fout;
                }else if (infile=="def") {
                    print $0 >> def;
                }else if (infile=="inc"){
                    print $0 >> inc;
                }else print $0 >> out;
               next;
               }

Answer 3

in case you are finding difficult to extract function names :

1> use ctags ( a program ) to extract function names . ctags -x --c-kinds=fp path_to_file. 2> once u got the function names, write a simple perl script to extract contents of function by passing the script name of function as said above.