URL Encoding/Decoding in C
Recently I had the need to encode and decode URL-encoded strings. After doing a brief search of what was available, I found that most of the code I was seeing wasn't terribly efficient and/or was rather poorly written. I decided to whip up my own routines and am sharing them here.
To the extent possible under law,
Fred Bulback
has waived all copyright and related or neighboring rights to
URL Encoding/Decoding in C.
This work is published from:
United States.
/* Converts a hex character to its integer value */
char from_hex(char ch) {
return isdigit(ch) ? ch - '0' : tolower(ch) - 'a' + 10;
}
/* Converts an integer value to its hex character*/
char to_hex(char code) {
static char hex[] = "0123456789abcdef";
return hex[code & 15];
}
/* Returns a url-encoded version of str */
/* IMPORTANT: be sure to free() the returned string after use */
char *url_encode(char *str) {
char *pstr = str, *buf = malloc(strlen(str) * 3 + 1), *pbuf = buf;
while (*pstr) {
if (isalnum(*pstr) || *pstr == '-' || *pstr == '_' || *pstr == '.' || *pstr == '~')
*pbuf++ = *pstr;
else if (*pstr == ' ')
*pbuf++ = '+';
else
*pbuf++ = '%', *pbuf++ = to_hex(*pstr >> 4), *pbuf++ = to_hex(*pstr & 15);
pstr++;
}
*pbuf = '\0';
return buf;
}
/* Returns a url-decoded version of str */
/* IMPORTANT: be sure to free() the returned string after use */
char *url_decode(char *str) {
char *pstr = str, *buf = malloc(strlen(str) + 1), *pbuf = buf;
while (*pstr) {
if (*pstr == '%') {
if (pstr[1] && pstr[2]) {
*pbuf++ = from_hex(pstr[1]) << 4 | from_hex(pstr[2]);
pstr += 2;
}
} else if (*pstr == '+') {
*pbuf++ = ' ';
} else {
*pbuf++ = *pstr;
}
pstr++;
}
*pbuf = '\0';
return buf;
}
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