Quote as argument to macro 
Author Message
 Quote as argument to macro

I'm trying to write some code that replaces an escape sequence in a
string with the appropriate character, e.g. that would replace "\\n"
with "\n", or that would change a file consisting of a backslash and the
letter 'n' to the newline character.  To make life easier on myself,
I've written a macro to quickly test for a given escape sequence, and
it's my first attempt to use the token pasting operator ##.

Here's the smallest code that should compile that demonstrates my

#include <stdio.h>

#define TRY_ESCAPE(x) if (c == '##x##') *currentPtr++= '\##x##'

int main(void) {
    int c=0;
    char escapedString[512]={0};
    char* currentPtr=escapedString;
    int isEscaped=0;
    while (c != EOF || currentPtr >= &escapedString[511]) {
      if (isEscaped) {
        if (c==EOF) fatalError("Unexpected \\");
        else TRY_ESCAPE(");
        else TRY_ESCAPE(');
        else TRY_ESCAPE(\);
        else TRY_ESCAPE(a);
        else TRY_ESCAPE(b);
        else TRY_ESCAPE(f);
        else TRY_ESCAPE(n);
        else TRY_ESCAPE(r);
        else TRY_ESCAPE(t);
        else TRY_ESCAPE(v);
        else {
          char error[32];
          sprintf(error, "Unknown escape sequence \\%c", c);
      else if (c=='\\') {
      else if (c != EOF) *currentPtr++=c;
   return 0;


This code produces the following errors:

test.c:26:49: missing terminating " character
test.c:14:35: possible start of unterminated string literal
test.c:36:1: unterminated argument list invoking macro "TRY_ESCAPE"

I also recognize that even if I solve this prolem, TRY_ESCAPE(") would
produce the code

if (c == '"') *currentPtr++= '\"'

which doesn't correctly escape the first quote.

How can I accomplish what I want?  Thanks for any help.


Sun, 05 Dec 2004 02:12:39 GMT  
 [ 1 post ] 

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