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Browse - programming tips - c encode filename for url

Date: 2011jun25
Language: C/C++


Q.  How do I encode a file name to be a URL?

A.  Here are two routines that can do that:

// Helper function
inline char * Shuffle(char * dest, const char * src)
{
	return (char *) memmove(dest, src, strlen(src) + sizeof(char));
}

void EncodeForUrl(char * s)
{
	char			szHex[] = "%??";		// We depend on the percent symbol at szHex[0]
	const int		lenHex = strlen(szHex);

	if (s == NULL) return;

	for (char * p = s; *p;)
	{
		if (isalnum(*p)))
		{
			p++;
		}
		else
		{
			Shuffle(p+lenHex, p+1);
			sprintf(szHex+1, "%02X", *p);
			memcpy(p, szHex, lenHex);
			p += lenHex;
		}
	}
}

// Turn %3A into colon, and %5C into backslash, etc
void DecodeFromUrl(char * s)
{
	char	szHex[] = "??";		// We depend on the NUL character at szHex[2]
	char *	dummy;

	if (s == NULL) return;

	for (char * p = s; *p; p++)
	{
		if (*p == '%')
		{
			szHex[0] = p[1];
			szHex[1] = p[2];
			*p = (char) strtol(szHex, &dummy, 16);
			Shuffle(p+1, p+3);
		}
	}
}

void ExampleUse()
{
	// Make a URL with a filename
	char	filename[MAX_PATH] = "c:\\windows\\fonts\\arial.ttf";
	char	url[MAX_PATH*3];

	EncodeForUrl(filename);
	_snprintf(url, sizeof(url), "dosomething.cgi?filename=%s", filename);
}

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