Programming Forums > Application Development > C

Sane · Mar 20th, 2008, 2:25 PM

Here we go. The only other thing that I can see of concern is if dest is attempted to be written to past the end of the array. But since I don't personally need to watch out for that, I'm leaving out a length restriction. I'm just warning anyone who stumbles across this thread and finds the code, to be careful that dest isn't written to past the end of the array.

 C Syntax (Toggle Plain Text) 
#include <stdio.h>
#include <string.h>
 
int c_isalnum(const char c) {
    return c>='0'&&c<='9' || c>='a'&&c<='z' || c>='A'&&c<='Z';
}
 
int urlencode(char *dest, const char *src) {
    /* urlencode all non-alphanumeric characters in the C-string 'src'
       store result in the C-string 'dest'
       return the length of the url encoded C-string
    */
    char *d;
    int i;
    for(i=0, d=dest; src[i]; i++) {
        if(c_isalnum(src[i])) *(d++) = src[i];
        else {
            sprintf(d, "%%%02X", src[i]);
            d += 3;
        }
    }   
    *d = 0;
    return d-dest;
}
 
int main() {
    char buff[1024];
    int len;
 
    len = urlencode(buff, "Hello 2 The World! $%^&*()");
    printf("[%d] %s\n", len, buff);
 
    return 0;
}
#include <stdio.h>
#include <string.h>

int c_isalnum(const char c) {
    return c>='0'&&c<='9' || c>='a'&&c<='z' || c>='A'&&c<='Z';
}

int urlencode(char *dest, const char *src) {
    /* urlencode all non-alphanumeric characters in the C-string 'src'
       store result in the C-string 'dest'
       return the length of the url encoded C-string
    */
    char *d;
    int i;
    for(i=0, d=dest; src[i]; i++) {
        if(c_isalnum(src[i])) *(d++) = src[i];
        else {
            sprintf(d, "%%%02X", src[i]);
            d += 3;
        }
    }   
    *d = 0;
    return d-dest;
}

int main() {
    char buff[1024];
    int len;
    
    len = urlencode(buff, "Hello 2 The World! $%^&*()");
    printf("[%d] %s\n", len, buff);

    return 0;
}

Ancient Dragon · Mar 20th, 2008, 2:29 PM

When I compiled and ran your program this is what I got (VC++ 2008 Express on Vista)

Quote:

[50] Hello%202%20The%20World%21%20%24%25%5E%26%2A%28%29
Press any key to continue . . .

Sane · Mar 20th, 2008, 2:34 PM

That looks right. Thanks.

Jessehk · Mar 20th, 2008, 5:46 PM

Is there a particular reason you didn't use isalnum() from ctype.h and wrote your own?

Sane · Mar 20th, 2008, 8:42 PM

It's C99. But I need things to be as compatible as possible. I'll also be asking you people to help me translate some snippets (this included) to Java and other languages. You guys will see why in 1 or 2 days. I think Infinate knows why.

Jessehk · Mar 20th, 2008, 8:49 PM

Quote:

Originally Posted by Sane

It's C99. But I need things to be as compatible as possible.

It isn't, AFAIK. But even if it was (and I'm wrong), you could just do

 c Syntax (Toggle Plain Text) 
isalpha(ch) || isdigit(ch)
isalpha(ch) || isdigit(ch)

According to my man-pages, all of the functions in ctype.h are actually macros that do table lookups. They're fairly efficient (probably more so than your function), and I don't see any reason to not use them.

Ancient Dragon · Mar 20th, 2008, 9:06 PM

Quote:

Originally Posted by Sane

It's C99. :

No -- its been around for many many years, as far back as I remember.

Sane · Mar 20th, 2008, 11:52 PM

Oh, I just checked. It isn't C99. I was just thrown off by Ooble who said "It is". Sorry.

Ooble · Mar 21st, 2008, 2:02 AM

I thought you meant "is it part of C99?" not "was it introduced by C99?" Apologies for the confusion.

Mar 20th, 2008, 2:25 PM	#11
Sane Banned Join Date: Apr 2005 Location: Waterloo, Ontario Posts: 2,101 Rep Power: 6	Re: How Do I Urlencode A String In C? Here we go. The only other thing that I can see of concern is if dest is attempted to be written to past the end of the array. But since I don't personally need to watch out for that, I'm leaving out a length restriction. I'm just warning anyone who stumbles across this thread and finds the code, to be careful that dest isn't written to past the end of the array. C Syntax (Toggle Plain Text) #include <stdio.h> #include <string.h> int c_isalnum(const char c) { return c>='0'&&c<='9' \|\| c>='a'&&c<='z' \|\| c>='A'&&c<='Z'; } int urlencode(char dest, const char src) { /* urlencode all non-alphanumeric characters in the C-string 'src' store result in the C-string 'dest' return the length of the url encoded C-string / char d; int i; for(i=0, d=dest; src[i]; i++) { if(c_isalnum(src[i])) (d++) = src[i]; else { sprintf(d, "%%%02X", src[i]); d += 3; } } d = 0; return d-dest; } int main() { char buff[1024]; int len; len = urlencode(buff, "Hello 2 The World! $%^&()"); printf("[%d] %s\n", len, buff); return 0; } #include <stdio.h> #include <string.h> int c_isalnum(const char c) { return c>='0'&&c<='9' \|\| c>='a'&&c<='z' \|\| c>='A'&&c<='Z'; } int urlencode(char dest, const char src) { / urlencode all non-alphanumeric characters in the C-string 'src' store result in the C-string 'dest' return the length of the url encoded C-string / char d; int i; for(i=0, d=dest; src[i]; i++) { if(c_isalnum(src[i])) (d++) = src[i]; else { sprintf(d, "%%%02X", src[i]); d += 3; } } d = 0; return d-dest; } int main() { char buff[1024]; int len; len = urlencode(buff, "Hello 2 The World! $%^&*()"); printf("[%d] %s\n", len, buff); return 0; } __________________ 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.

Mar 20th, 2008, 2:34 PM	#13
Sane Banned Join Date: Apr 2005 Location: Waterloo, Ontario Posts: 2,101 Rep Power: 6	Re: How Do I Urlencode A String In C? That looks right. Thanks. __________________ 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. Last edited by Sane; Mar 20th, 2008 at 2:44 PM.

Mar 20th, 2008, 5:46 PM	#14
Jessehk The Oblivious One Join Date: May 2005 Location: Ontario, Canada Posts: 648 Rep Power: 4	Re: How Do I Urlencode A String In C? Is there a particular reason you didn't use isalnum() from ctype.h and wrote your own? __________________ Dr. Zoidberg: [ecstatic] I'm going to a movie... with FRIENDS!

Mar 20th, 2008, 8:42 PM	#15
Sane Banned Join Date: Apr 2005 Location: Waterloo, Ontario Posts: 2,101 Rep Power: 6	Re: How Do I Urlencode A String In C? It's C99. But I need things to be as compatible as possible. I'll also be asking you people to help me translate some snippets (this included) to Java and other languages. You guys will see why in 1 or 2 days. I think Infinate knows why. __________________ 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.

Mar 20th, 2008, 11:52 PM	#18
Sane Banned Join Date: Apr 2005 Location: Waterloo, Ontario Posts: 2,101 Rep Power: 6	Re: How Do I Urlencode A String In C? Oh, I just checked. It isn't C99. I was just thrown off by Ooble who said "It is". Sorry. __________________ 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.

Mar 21st, 2008, 2:02 AM	#19
Ooble I eat cake for breakfast. Join Date: Jul 2004 Location: In my box. Posts: 4,434 Rep Power: 9	Re: How Do I Urlencode A String In C? I thought you meant "is it part of C99?" not "was it introduced by C99?" Apologies for the confusion. __________________ Me :: You :: Them

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Programming Forums > Application Development > C

How Do I Urlencode A String In C?