小编Cra*_*her的帖子

Edit1: rob mayoff'answer很精彩.这是我自己的:

    -(NSData *)change:(NSString *)hexString
    {
        int j=0;
        Byte bytes[[hexString length]];  
        for(int i=0;i<[hexString length];i++)
        {
            int int_ch;  

        unichar hex_char1 = [hexString characterAtIndex:i]; 
        int int_ch1;
        if(hex_char1 >= '0' && hex_char1 <='9')
            int_ch1 = (hex_char1-48)*16;   
        else if(hex_char1 >= 'A' && hex_char1 <='F')
            int_ch1 = (hex_char1-55)*16; 
        else 
            int_ch1 = (hex_char1-87)*16; 
        i++;

        unichar hex_char2 = [hexString characterAtIndex:i]; 
        int int_ch2;
        if(hex_char2 >= '0' && hex_char2 <='9')
            int_ch2 = (hex_char2-48); 
        else if(hex_char1 >= 'A' && hex_char1 <='F')
            int_ch2 = hex_char2-55; 
        else 
            int_ch2 = hex_char2-87; 

        int_ch …