How to extract a C function definition from a C source file
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From: megarajan on 1 Apr 2008 08:03 hi, Could anyone tell me the way to extract a C function definition from a C source file ? i.e search print1 should give me the output void print1() { } when the file is void print1() { } void print2() { } ..... Thanks Thanks Megarajan
From: Ed Morton on 1 Apr 2008 08:26 On 4/1/2008 7:03 AM, megarajan(a)gmail.com wrote: > hi, > > Could anyone tell me the way to extract a C function definition from a > C source file ? > > i.e search print1 should give me the output > > void print1() > { > > } > > when the file is > > void print1() > { > > } > > void print2() > { > > > } > > .... > > Thanks > Thanks > Megarajan With exactly that format of input file you could use: awk -v fn="print1" '$2==fn"()",/^}/' file Regards, Ed.
From: pk on 1 Apr 2008 08:53 megarajan(a)gmail.com wrote: > hi, > > Could anyone tell me the way to extract a C function definition from a > C source file ? > > i.e search print1 should give me the output > > void print1() > { > > } > > when the file is > > void print1() > { > > } > > void print2() > { > > > } > > .... > > Thanks > Thanks > Megarajan The following assumes balanced braces, and that the closing } for a function is the last character in its line. $ cat extract.awk function match_braces() { s=$0 # how to abuse gsub op=gsub(/{/,"",s); cl=gsub(/}/,"",s); if (op || cl) f=1; return (op-cl); } /void print1/ {ok=1} ok {n+=match_braces(); print; if ((n==0)&&(f==1)) exit} $ cat file.c #include <stdio.h> #include <stdlib.h> void print1() { int foo=1; int i,j,k,bar=2; if (foo==bar) { printf("hello, world\n"); } else { printf("Bye\n"); } for (i=0;i<10;i++) { for (j=0;j<10;j++) { for (k=0;k<10;k++) { printf("a"); } } } foo=110; } void print2() { } $ awk -f extract.awk file.c void print1() { int foo=1; int i,j,k,bar=2; if (foo==bar) { printf("hello, world\n"); } else { printf("Bye\n"); } for (i=0;i<10;i++) { for (j=0;j<10;j++) { for (k=0;k<10;k++) { printf("a"); } } } foo=110; } -- All the commands are tested with bash and GNU tools, so they may use nonstandard features. I try to mention when something is nonstandard (if I'm aware of that), but I may miss something. Corrections are welcome.
From: Ed Morton on 1 Apr 2008 08:47 On 4/1/2008 7:26 AM, Ed Morton wrote: > On 4/1/2008 7:03 AM, megarajan(a)gmail.com wrote: > >>hi, >> >>Could anyone tell me the way to extract a C function definition from a >>C source file ? >> >>i.e search print1 should give me the output >> >>void print1() >>{ >> >>} >> >>when the file is >> >>void print1() >>{ >> >>} >> >>void print2() >>{ >> >> >>} >> >>.... >> >>Thanks >>Thanks >>Megarajan > > > With exactly that format of input file you could use: > > awk -v fn="print1" '$2==fn"()",/^}/' file > In reality, of course, your code won't alaways have exactly that format, so you'll probably need to run a C beautifier to get your code into a standard format (e.g. "indent", "cb", "bcpp", "prettyprint" or "uncrustify" - google "C beautifier" or see the man pages and http://uncrustify.sourceforge.net/) and use a C parser like "cscope" (see http://cscope.sourceforge.net/) to find the function definition. Do NOT trust any shell/sed/perl/awk/whatever script that claims to understand C code without actually implementing a full C parser. Ed.
From: Ed Morton on 1 Apr 2008 10:08
On 4/1/2008 7:53 AM, pk wrote: > megarajan(a)gmail.com wrote: > > >>hi, >> >>Could anyone tell me the way to extract a C function definition from a >>C source file ? <snip> > The following assumes balanced braces, and that the closing } for a function > is the last character in its line. Abandon hope all ye who enter here ;-). I know, the code you posted will work for exactly the sample input but there's just WAY too many variations for how a function could be defined to try to handle them in general without a C parser. For example: void print1() { } void /* comment */ print1() { } int print1() { /* commented brace { */ } #if SOMETHING int #else void #endif print1() { } void print1(char arg) /* ANSI C arg */ { } void print1(arg) /* K&R C arg */ char arg; { } void print1(char); /* function template */ etc.... If the OP doesn't mind losing the comments you can strip those and the preprocessor stuff out using a preprocessor like "gcc -E" but there's still a ton of variations and it's not clear that'd be acceptable in this case anyway. It's much easier and more reliable to use a tool like cscope that's designed for parsing C, though that still needs some post-processing help to pull out the whole function rather than just the start of the definition. Ed. |