转换字节为百分比

Question

I want to convert bytes to a percentage. The percentage will represent the total amount a file that has been uploaded.

For example, I have:

int64_t totalBytesSent
int64_t totalBytesExpectedToSend

I want to convert that into a percentage (float).

I've tried this:

int64_t percentage = totalBytesSent/totalBytesExpectedToSend;

and this:

[NSNumber numberWithLongLong:totalBytesSent];
[NSNumber numberWithLongLong:totalBytesExpectedToSend];
CGFloat = [totalBytesSent longLongValue]/[totalBytesExpectedToSend longLongValue];

I think I am missing something in trying to do 'byte-math'. Does anyone know how to convert bytes to a percentage?

Answer 1

As long as you divide one integer value (doesn't matter which size of integer) by a bigger integer value the result will always be 0.

Either multiply the totalBytesSent value with 100 before dividing if you don't need decimals or convert values to a floating point value before doing the division.

The following code will result in the percentage as a value between 0 and 100:

int64_t percentage = totalBytesSent*100/totalBytesExpectedToSend;

Answer 2

You were close with:

int64_t percentage = totalBytesSent/totalBytesExpectedToSend;

This would return a number between 0 and 1...but you're doing math with integers. Cast one of them to a CGFloat , float , double , etc, then multiply it by 100, or multiply totalBytesSent by 100 before dividing if you don't want to do floating-point math:

int64_t percentage = (double)totalBytesSent/totalBytesExpectedToSend * 100;    //uses floating point math, slower
//or
int64_t percentage = totalBytesSent*100/totalBytesExpectedToSend;  //integer division, faster

Also, why are you using int64 for absolutely everything? Do you really need to send exabytes of data? unsigned would probably be the best choice:

unsigned totalBytesSent
unsigned totalBytesExpectedToSend

unsigned percentage = totalBytesSent*100/totalBytesExpectedToSend;

If you want a decimal point in your percentage, use floating-point math to divide and store the result in a floating-point type:

CGFloat percentage = totalBytesSent*100/totalBytesExpectedToSend;