Copies a string, replacing unprintable and some punctuation characters with their C-escaped versions.

c_encode_string.c

/**
 * Copies a string from 'in' to 'out', replacing unprintable and some
 * punctuation characters with their escaped versions.
 *              
 * To be safe, the output buffer should be allocated with (4 * ilen) characters
 * of space, for the worst case scenario, where all characters are unprintable.
 *          
 * @param ilen the length of the input string
 * @param in the input string
 * @param olen the length of the output buffer
 * @param out the output buffer 
 *
 * @return the number of characters copied
 */     
int _c_encode_string(int ilen, char in[ilen], int olen, char out[olen])
{
    int pos = 0;

    for (int i = 0; i < ilen && pos < olen; i++) {
        char c = in[i];
        if (isprint(c) && !ispunct(c)) {
            out[pos++] = c;
        } else { 
            switch (c) { 
            case '\a': out[pos++] = '\\'; out[pos++] =  'a'; break;
            case '\b': out[pos++] = '\\'; out[pos++] =  'b'; break;
            case '\f': out[pos++] = '\\'; out[pos++] =  'f'; break;
            case '\n': out[pos++] = '\\'; out[pos++] =  'n'; break;
            case '\r': out[pos++] = '\\'; out[pos++] =  'r'; break;
            case '\t': out[pos++] = '\\'; out[pos++] =  't'; break;
            case '\v': out[pos++] = '\\'; out[pos++] =  'v'; break;
            case '\"': out[pos++] = '\\'; out[pos++] = '\"'; break;
            default:
                if (ispunct(c)) out[pos++] = c;
                else pos += sprintf(&out[pos], "\\%03o", c);
                break;
            }
        }
    }   
            
    out[pos] = 0;
            
    return pos;
}