十六进制和字符串相互转换

//将十六进制的字符串转换成NSString则可使用如下方式:
+ (NSString *)convertHexStrToString:(NSString *)str {
if (!str || [str length] == 0) {
return nil;
}

NSMutableData *hexData = [[NSMutableData alloc] initWithCapacity:8];
NSRange range;
if ([str length] % 2 == 0) {
range = NSMakeRange(0, 2);
} else {
range = NSMakeRange(0, 1);
}
for (NSInteger i = range.location; i < [str length]; i += 2) {
unsigned int anInt;
NSString *hexCharStr = [str substringWithRange:range];
NSScanner *scanner = [[NSScanner alloc] initWithString:hexCharStr];

[scanner scanHexInt:&anInt];
NSData *entity = [[NSData alloc] initWithBytes:&anInt length:1];
[hexData appendData:entity];

range.location += range.length;
range.length = 2;
}
NSString *string = [[NSString alloc]initWithData:hexData encoding:NSUTF8StringEncoding];
return string;
}

//将NSString转换成十六进制的字符串则可使用如下方式:
+ (NSString *)convertStringToHexStr:(NSString *)str {
if (!str || [str length] == 0) {
return @"";
}
NSData *data = [str dataUsingEncoding:NSUTF8StringEncoding];

NSMutableString *string = [[NSMutableString alloc] initWithCapacity:[data length]];

[data enumerateByteRangesUsingBlock:^(const void *bytes, NSRange byteRange, BOOL *stop) {
unsigned char *dataBytes = (unsigned char*)bytes;
for (NSInteger i = 0; i < byteRange.length; i++) {
NSString *hexStr = [NSString stringWithFormat:@"%x", (dataBytes[i]) & 0xff];
if ([hexStr length] == 2) {
[string appendString:hexStr];
} else {
[string appendFormat:@"0%@", hexStr];
}
}
}];

return string;
}