Objective-C中的二进制转换算法

Question

How do I get the value of a certain bit from a byte or integer? The only similar answer that I've been able to find is for a specific character inside a string. I am trying to convert a binary number to a decimal number, and perhaps there is a much simpler way to do this, but I was thinking of this: multiplying 2^(position of integer from right) by either a 1 or 0, depending on the value of the integer at the position previously mentioned. Any tips?

Answer 1

NSString * binary = @"0011010";
long value = strtol([b UTF8String], NULL, 2);

Answer 2

There are multiways of obtaining the value of bit within a byte or integer. It all depends on your needs.

One way would be to use a mask with bitwise operators.

int result = sourceValue & 8;    // 8 ->  0x00001000
// result non zero if the 4th bit from the right is ON.

You can also shift bits one by one and read, say, the right-most bit.

for (int i = 0;  i < 8; i++)
    NSLog(@"Bit %d is %@", i, (sourceValue % 2 == 0) ? @"OFF" : @"ON");
    sourceValue = sourceValue >> 1;  // shift bits to the right for next loop.
}

Or if you just want the text representation for an integer, you could let NSNumber do the work:

NSString* myString = [[NSNumber numberWithInt:sourceValue] stringValue];