Programming Forums > Application Development > C

angel face · Feb 28th, 2008, 6:42 PM

Hello guys.

just wondering if you can help.

If i have a C char array:

char word = "he?llo?";

Before i print it out, i want to insert a backslash before any question marks. (im working on a regular expressions program so i want to escape the ? metacharacter with a backslash).

i want to manipulate it so when print the above out it will look like this:
he\?llo\?

does anyone know how this can be done?
id really appreciate it...

thanks a mill

Narue · Feb 28th, 2008, 7:21 PM

Escape it:

 c Syntax (Toggle Plain Text) 
char word = "he\\?llo\\?";
char word = "he\\?llo\\?";

OpenLoop · Feb 28th, 2008, 7:29 PM

@Narue: I think 'word' here intended to be a user input.

@angel face: since you're not using C++, you can't use the string class. Too bad. What you can do is read the string one char at a time and copy it to another one replacing the ? with /?:

 c Syntax (Toggle Plain Text) 
char word[] = "he?llo?";
char newWord[100];
int i = 0, j = 0;
for(i = 0; i < 7 i++)
{
  if(word[i] == '?')   newWord[j++] = '\';
  newWord[j++] = word[i];
}
 
char word[] = "he?llo?";
char newWord[100];
int i = 0, j = 0;
for(i = 0; i < 7 i++)
{
  if(word[i] == '?')   newWord[j++] = '\';
  newWord[j++] = word[i];
}

Narue · Feb 28th, 2008, 7:55 PM

>@Narue: I think 'word' here intended to be a user input
And your point is?

>if(word[i] == '?') newWord[j++] = '\';
The solution is identical, escape a backslash to print a backslash. Your example wouldn't compile because the character isn't properly terminated:

 c Syntax (Toggle Plain Text) 
if(word[i] == '?') newWord[j++] = '\\';
if(word[i] == '?') newWord[j++] = '\\';

Sane · Feb 28th, 2008, 8:38 PM

OpenLoop, you're missing a semi-colon in your for loop. As Narue pointed out, you don't escape the backslash. And you need to null-terminate the string as well. The following modification will null-terminate, and not be limited to words of length 7.

(Toggle Plain Text)

len = strlen(word);
for(i=0, j=0; i < len; i++) {
    if(word[i] == '?') newWord[j++] = '\\';
    newWord[j++] = word[i];
}
newWord[j] = '\0';

Alternatively, i <= len can be used to implicitely null-terminate.

OpenLoop · Feb 29th, 2008, 12:36 AM

Quote:

Originally Posted by Narue

And your point is?

you can't hardcode a slash in there. I understand that you provided a way to do it rather than a method, but I was under the impression the OP was looking for the latter (I could be wrong).

@Sane: thanks for the correction. I knew that highlighting didn't look right!

Feb 28th, 2008, 6:42 PM	#1
angel face Newbie Join Date: Feb 2008 Posts: 3 Rep Power: 0	C char array....need help! Hello guys. just wondering if you can help. If i have a C char array: (Toggle Plain Text) char word = "he?llo?"; char word = "he?llo?"; Before i print it out, i want to insert a backslash before any question marks. (im working on a regular expressions program so i want to escape the ? metacharacter with a backslash). i want to manipulate it so when print the above out it will look like this: he\?llo\? does anyone know how this can be done? id really appreciate it... thanks a mill

Feb 28th, 2008, 7:21 PM	#2
Narue Professional Programmer Join Date: Sep 2005 Posts: 419 Rep Power: 4	Re: C char array....need help! Escape it: c Syntax (Toggle Plain Text) char word = "he\\?llo\\?"; char word = "he\\?llo\\?"; __________________ Even if the voices aren't real, they have some pretty good ideas.

Feb 28th, 2008, 7:29 PM	#3
OpenLoop Expert Programmer Join Date: May 2005 Location: East Lansing, MI Posts: 663 Rep Power: 4	Re: C char array....need help! @Narue: I think 'word' here intended to be a user input. @angel face: since you're not using C++, you can't use the string class. Too bad. What you can do is read the string one char at a time and copy it to another one replacing the ? with /?: c Syntax (Toggle Plain Text) char word[] = "he?llo?"; char newWord[100]; int i = 0, j = 0; for(i = 0; i < 7 i++) { if(word[i] == '?') newWord[j++] = '\'; newWord[j++] = word[i]; } char word[] = "he?llo?"; char newWord[100]; int i = 0, j = 0; for(i = 0; i < 7 i++) { if(word[i] == '?') newWord[j++] = '\'; newWord[j++] = word[i]; }

Feb 28th, 2008, 7:55 PM	#4
Narue Professional Programmer Join Date: Sep 2005 Posts: 419 Rep Power: 4	Re: C char array....need help! >@Narue: I think 'word' here intended to be a user input And your point is? >if(word[i] == '?') newWord[j++] = '\'; The solution is identical, escape a backslash to print a backslash. Your example wouldn't compile because the character isn't properly terminated: c Syntax (Toggle Plain Text) if(word[i] == '?') newWord[j++] = '\\'; if(word[i] == '?') newWord[j++] = '\\'; __________________ Even if the voices aren't real, they have some pretty good ideas.

Feb 28th, 2008, 8:38 PM	#5
Sane Programming Guru Join Date: Apr 2005 Location: Waterloo, Ontario Posts: 2,035 Rep Power: 6	Re: C char array....need help! OpenLoop, you're missing a semi-colon in your for loop. As Narue pointed out, you don't escape the backslash. And you need to null-terminate the string as well. The following modification will null-terminate, and not be limited to words of length 7. (Toggle Plain Text) len = strlen(word); for(i=0, j=0; i < len; i++) { if(word[i] == '?') newWord[j++] = '\\'; newWord[j++] = word[i]; } newWord[j] = '\0'; len = strlen(word); for(i=0, j=0; i < len; i++) { if(word[i] == '?') newWord[j++] = '\\'; newWord[j++] = word[i]; } newWord[j] = '\0'; Alternatively, `i <= len` can be used to implicitely null-terminate. __________________ Looking for tough programming challenges? Try participating in Sane's Monthly Algorithms Challenges! Composing Techno is a little side hobby of mine. Techno by DJ Sane. All free for download.

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Programming Forums > Application Development > C

C char array....need help!