字符串与十六进制的相互转换

// 十六进制转换成字符串

+(NSString*)dataToHexString:(NSData*)data {
    if (data == nil) {
        return @"";
    }
    Byte *dateByte = (Byte *)[data bytes];
    NSString *hexStr=@"";
    for(int i=0;i<[data length];i++) {
        NSString *newHexStr = [NSString stringWithFormat:@"%x",dateByte[i]&0xff]; ///16进制数
        if([newHexStr length]==1)
            hexStr = [NSString stringWithFormat:@"%@0%@",hexStr,newHexStr];
        else
            hexStr = [NSString stringWithFormat:@"%@%@",hexStr,newHexStr];
    }
    return hexStr;
}

//字符串转换十六进制 比如 FF ->0XFF

-(NSData*)convert:(NSString*)str{
    const char* cs = str.UTF8String;
    int count = (int)strlen(cs);
    int8_t  bytes[count / 2];
    for(int i = 0; i<count; i+=2){
        char c1 = *(cs + i);
        char c2 = *(cs + i + 1);
        if(C2I(c1) >= 0 && C2I(c2) >= 0){
            bytes[i / 2] = C2I(c1) * 16 + C2I(c2);
            
        }else{
            return nil;
        }
    }
    return [NSData dataWithBytes:bytes length:count /2];

}