谁能告诉我该功能的影响？

Question

The first method is:

-(NSData *)stringToAddBytes:(NSString*)addString
{
    int length = (int)[addString length];
    if(length < 2)
    {
        return nil;
    }
    Byte buf[length / 2];
    for(int i = 0 ;i < length/2 ;i++)
    {
        NSString *str = [addString substringWithRange:NSMakeRange(i * 2, 2)];
        Byte b = [self hexStringToByte:str];
        buf[i]=b;
    }

    NSData * myD = [[NSData alloc]initWithBytes:buf length:length/2];
    return myD;
}

THe method that the first method called.

-(Byte)hexStringToByte:(NSString*)str
{
    NSArray *charArray = [[NSArray alloc]initWithObjects:@"0",@"1",@"2",@"3",@"4",@"5",@"6",@"7",@"8",@"9",
                          @"A",@"B",@"C",@"D",@"E",@"F",nil];
    NSString *str1 = [str substringWithRange:NSMakeRange(0, 1)];
    int num1 = (int)[charArray indexOfObject:str1];
    NSString *str2 = [str substringWithRange:NSMakeRange(1, 1)];
    int num2 = (int)[charArray indexOfObject:str2];

    Byte b = num1*16+num2;
    return b;
}

Thank you for your answer.It looks change large char to small char.

Answer 1

hexStringToByte: wil convert string with hexadecimal number representation (example @"FF") to Byte value (in this example 255).

stringToAddBytes: uses hexStringToByte: to create NSData of bytes breaking addString into two letter peases and converting them to Byte values.

In other words, this is string serialization.

Example:

// 255 = 0xFF
// 170 = 0xAA
// 136 = 0x88
NSString* addString = @"FFAA88";
NSData* data = [self stringToAddBytes:addString];
// data will be [255, 170, 136]

Be aware that NSData is not an array, instead, it represents a raw object.