Removing a C ++ comment from source

Question

I have C ++ code with /* */and style comments //. I want to have a way to delete them automatically. Apparently, the use of the editor (for example, ultraedit) with some regular expression to search for /*, */and //should carry out the task. But upon closer inspection, a complete solution is not so simple, because the sequences / * or // may not represent a comment if they are inside another comment, a string literal, or a character literal. eg.

printf(" \" \" " "  /* this is not a comment and is surrounded by an unknown number of double-quotes */");

- a sequence of comments inside a double quote. And it's not an easy task to determine if a string is inside a pair of valid double quotes. Although it is

// this is a single line comment /* <--- this does not start a comment block 
// this is a second comment line with an */ within

is a sequence of comments in other comments.

Is there a more complete way to remove comments from a C ++ source, given a string literal and a comment? For example, is it possible to instruct the preprocessor to delete comments until it executes, say, the #include directive?

Answer 1

Let someone vote for my own answer to my own question.

Thanks to the idea of ​​Martin York, I found that in Visual Studio the solution looks very simple (subject to further testing). Just rename ALL preprocessor directives to something else (something invalid C ++ syntax is fine) and use cl.exe with / P

cl target.cpp /P

a target.i. . , . , #line, cl.exe.

, , MSDN, :

. Trigraph .

, () , ​​ , . , , .

. . .

. #include , .

escape- . Microsoft C ++ , ASCII.

. , "String" " ".

; .

Tokenization Preprocessing. , ( ), 3 .

.h, /FI, . .i .cpp .h. . # . . , , / , .

, - . ( ).

.

// vc8.cpp : Defines the entry point for the console application.
//

-#include "stdafx.h"
-#include <windows.h>
-#define NOERR
-#ifdef NOERR
  /* comment here */
 whatever error line is ok
-#else
  some error line if NOERR not defined
      // comment here
-#endif
void pr() ;
int _tmain(int argc, _TCHAR* argv[])
{
    pr();
    return 0;
}

/*comment*/

void pr() {
    printf(" /* "); /* comment inside string " */
    // comment terminated by \
    continue a comment line
    printf(" "); /** " " string inside comment */
    printf/* this is valid comment within line continuation */\
("some weird lines \
with line continuation");
}

cl.exe vc8.cpp /P cl.exe ( # )

#line 1 "vc8.cpp"



-#include "stdafx.h"
-#include <windows.h>
-#define NOERR
-#ifdef NOERR

 whatever error line is ok
-#else
  some error line if NOERR not defined

-#endif
void pr() ;
int _tmain(int argc, _TCHAR* argv[])
{
    pr();
    return 0;
}



void pr() {
    printf(" /* "); 


    printf(" "); 
    printf\
("some weird lines \
with line continuation");
}

Answer 2

C .

:

, MACROS #if

> cat t.cpp
/*
 * Normal comment
 */
// this is a single line comment /* <--- this does not start a comment block 
// this is a second comment line with an */ within
#include <stdio.h>

#if __SIZEOF_LONG__ == 4
int bits = 32;
#else
int bits = 16;
#endif

int main()
{
    printf(" \" \" " " /* this is not a comment and is surrounded by an unknown number of double-quotes */");
    /*
     * comment with a single // line comment enbedded.
     */
    int x;
    // A single line comment /* Normal enbedded */ Comment
}

, #if , .
. cpp -E -dM.

#defines , .

> cpp -E -dM t.cpp > /tmp/def
> cat /tmp/def t.cpp | sed -e s/^#inc/-#inc/ | cpp - | sed s/^-#inc/#inc/
# 1 "t.cpp"
# 1 "<built-in>"
# 1 "<command-line>"
# 1 "t.cpp"






#include <stdio.h>


int bits = 32;




int main()
{
    printf(" \" \" " " /* this is not a comment and is surrounded by an unknown number of double-quotes */");    



    int x;

}

Answer 3

SD ++ Formatter . ++ , , , , .

, , . Formatter .

Answer 4

(, boost:: spirit) . , , . , , .

Answer 5

The regular expression is not intended for parsing languages; it is, at best, an unsuccessful attempt.

To do this, you need a full-sized parser. You might want to consider Clangrewriting is the clear purpose of the Clang library set, and there are already existing rewriting devices from which you can get inspiration.

Answer 6

#include <iostream>
#include<fstream>
using namespace std;

int main() {
    ifstream fin;
    ofstream fout;
    fin.open("input.txt");
    fout.open("output.txt");
    char ch;
    while(!fin.eof()){
        fin.get(ch);
        if(ch=='/'){
            fin.get(ch);
            if(ch=='/' )
            {   //cout<<"Detected\n";
                fin.get(ch);
                while(!(ch=='\n'||ch=='\0'))
                {
                //cout<<"while";
                fin.get(ch);
                }
            }
            if(ch=='*')
            {
                fin.get(ch);
                while(!(ch=='*')){
                    fin.get(ch);
                }
                fin.get(ch);
                if(ch=='/'){
                //  cout<<"Detected Multi-Line\n";
                    fin.get(ch);
                }

            }
        }
        fout<<ch;
    }
    return 0;
}