The following code is based on an IRI library I have been working on for awhile. Section 3.2 ("Converting URIs to IRIs") of RFC 3987 deals with converting invalid UTF-8 octets to valid UTF-8.
#define IS_IN_RANGE(c, f, l) (((c) >= (f)) && ((c) <= (l)))
int UTF8BufferToUTF32Buffer(char *Data, int DataLen, unsigned long *Buffer, int BufLen, int *Eaten)
{
if( Eaten )
{
*Eaten = 0;
}
int Result = 0;
unsigned char b, b2;
unsigned char *ptr = (unsigned char*) Data;
unsigned long uc;
int i = 0;
int seqlen;
while( i < DataLen )
{
if( (Buffer) && (!BufLen) )
break;
b = ptr[i];
if( (b & 0x80) == 0 )
{
uc = (unsigned long)(b & 0x7F);
seqlen = 1;
}
else if( (b & 0xE0) == 0xC0 )
{
uc = (unsigned long)(b & 0x1F);
seqlen = 2;
}
else if( (b & 0xF0) == 0xE0 )
{
uc = (unsigned long)(b & 0x0F);
seqlen = 3;
}
else if( (b & 0xF8) == 0xF0 )
{
uc = (unsigned long)(b & 0x07);
seqlen = 4;
}
else
{
uc = 0;
return -1;
}
if( (i+seqlen) > DataLen )
{
return -1;
}
for(int j = 1; j < seqlen; ++j)
{
b = ptr[i+j];
if( (b & 0xC0) != 0x80 )
{
return -1;
}
}
switch( seqlen )
{
case 2:
{
b = ptr[i];
if( !IS_IN_RANGE(b, 0xC2, 0xDF) )
{
return -1;
}
break;
}
case 3:
{
b = ptr[i];
b2 = ptr[i+1];
if( ((b == 0xE0) && !IS_IN_RANGE(b2, 0xA0, 0xBF)) ||
((b == 0xED) && !IS_IN_RANGE(b2, 0x80, 0x9F)) ||
(!IS_IN_RANGE(b, 0xE1, 0xEC) && !IS_IN_RANGE(b, 0xEE, 0xEF)) )
{
return -1;
}
break;
}
case 4:
{
b = ptr[i];
b2 = ptr[i+1];
if( ((b == 0xF0) && !IS_IN_RANGE(b2, 0x90, 0xBF)) ||
((b == 0xF4) && !IS_IN_RANGE(b2, 0x80, 0x8F)) ||
!IS_IN_RANGE(b, 0xF1, 0xF3) )
{
return -1;
}
break;
}
}
for(int j = 1; j < seqlen; ++j)
{
uc = ((uc << 6) | (unsigned long)(ptr[i+j] & 0x3F));
}
if( Buffer )
{
*Buffer++ = uc;
--BufLen;
}
++Result;
i += seqlen;
}
if( Eaten )
{
*Eaten = i;
}
return Result;
}
{
std::string filename = "...";
unsigned long ch;
int eaten;
std::string::size_type i = 0;
while( i < filename.length() )
{
if( UTF8BufferToUTF32Buffer(&filename[i], filename.length()-i, &ch, 1, &eaten) == 1 )
{
i += eaten;
}
else
{
// replace the character at filename[i] with your chosen
// escaping, and then increment i by the number of
// characters used...
}
}
}
In your case, all you have to do is decide what kind of escaping you want to use. URIs/IRIs uses percent-encoding ("%NN", where "NN" is the 2-digit hex value of an octet).