How to get file size properly and convert it to MB, GB in Cocoa? [duplicate]

Answer 1

If you're targeting OS X 10.8 or iOS 6, you can use NSByteCountFormatter.

I would write your example like this:

    NSError *error = nil;
    NSDictionary *attribs = [[NSFileManager defaultManager] attributesOfItemAtPath:path error:&error];
    if (attribs) {
        NSString *string = [NSByteCountFormatter stringFromByteCount:[attribs fileSize] countStyle:NSByteCountFormatterCountStyleFile];
        NSLog(@"%@", string);
    }

Answer 2

Here is a piece of code from my library. (I hereby release it under the simplified BSD license so there.) It is fairly extensively tested, and it does all the rounding exactly correct. This is not as trivial as it sounds. It always gives two significant figures unless it prints three digits (e.g., 980 B) in which case all three digits are significant.

Using stringWithFormat:@"%..something...f" won't work because if you round 999999 bytes up to 1000 kilobytes, you want to display it as 1.0 MB, not as 1000 kB.

Note that this code also does "banker's rounding" or "unbiased rounding" or "round to even", whichever you want to call it. So 1050 becomes "1.0 kB", but 1150 becomes "1.2 kB". This is the exact same way that printf does it on my system and is the generally preferred rounding method for this sort of thing.

#include <stdio.h>
#include <string.h>
#include <stdint.h>

#define SIZE_BUFSZ 7
static char const SIZE_PREFIXES[] = "kMGTPEZY";

void
format_size(char buf[SIZE_BUFSZ], uint64_t sz)
{
    int pfx = 0;
    unsigned int m, n, rem, hrem;
    uint64_t a;
    if (sz <= 0) {
        memcpy(buf, "0 B", 3);
        return;
    }
    a = sz;
    if (a < 1000) {
        n = a;
        snprintf(buf, SIZE_BUFSZ, "%u B", n);
        return;
    }
    for (pfx = 0, hrem = 0; ; pfx++) {
        rem = a % 1000ULL;
        a = a / 1000ULL;
        if (!SIZE_PREFIXES[pfx + 1] || a < 1000ULL)
            break;
        hrem |= rem;
    }
    n = a;
    if (n < 10) {
        if (rem >= 950) {
            buf[0] = '1';
            buf[1] = '0';
            buf[2] = ' ';
            buf[3] = SIZE_PREFIXES[pfx];
            buf[4] = 'B';
            buf[5] = '\0';
            return;
        } else {
            m = rem / 100;
            rem = rem % 100;
            if (rem > 50 || (rem == 50 && ((m & 1) || hrem)))
                m++;
            snprintf(buf, SIZE_BUFSZ,
                     "%u.%u %cB", n, m, SIZE_PREFIXES[pfx]);
        }
    } else {
        if (rem > 500 || (rem == 500 && ((n & 1) || hrem)))
            n++;
        if (n >= 1000 && SIZE_PREFIXES[pfx + 1]) {
            buf[0] = '1';
            buf[1] = '.';
            buf[2] = '0';
            buf[3] = ' ';
            buf[4] = SIZE_PREFIXES[pfx+1];
            buf[5] = 'B';
            buf[6] = '\0';
        } else {
            snprintf(buf, SIZE_BUFSZ,
                     "%u %cB", n, SIZE_PREFIXES[pfx]);
        }
    }
}

Here is the test data:

{ 0, "0 B" },
{ 5, "5 B" },
{ 20, "20 B" },
{ 100, "100 B" },
{ 500, "500 B" },
{ 999, "999 B" },
{ 1000, "1.0 kB" },
{ 1050, "1.0 kB" },
{ 1051, "1.1 kB" },
{ 2349, "2.3 kB" },
{ 2350, "2.4 kB" },
{ 9949, "9.9 kB" },
{ 9950, "10 kB" },
{ 10000, "10 kB" },
{ 10500, "10 kB" },
{ 10501, "11 kB" },
{ 99499, "99 kB" },
{ 99500, "100 kB" },
{ 999499, "999 kB" },
{ 999500, "1.0 MB" },
{ 1000000, "1.0 MB" },
{ 952500000, "952 MB" },
{ 952500001, "953 MB" },
{ 1000000000, "1.0 GB" },
{ 2300000000000ULL, "2.3 TB" },
{ 9700000000000000ULL, "9.7 PB" }

Answer 3

For converting file size to MB, Gb use below function

- (id)transformedValue:(id)value
{
    
    double convertedValue = [value doubleValue];
    int multiplyFactor = 0;
    
    NSArray *tokens = @[@"bytes",@"KB",@"MB",@"GB",@"TB",@“PB”, @“EB”, @“ZB”, @“YB”];
    
    while (convertedValue > 1024) {
        convertedValue /= 1024;
        multiplyFactor++;
    }
    
    return [NSString stringWithFormat:@"%4.2f %@",convertedValue, tokens[multiplyFactor]];
}

EDIT:

You can also use NSByteCountFormatter class. Available in iOS 6.0 / OS X v10.8 and later.

[NSByteCountFormatter stringFromByteCount:1999 countStyle:NSByteCountFormatterCountStyleFile];

You can use NSByteCountFormatterCountStyleFile, NSByteCountFormatterCountStyleMemory, NSByteCountFormatterCountStyleDecimal or NSByteCountFormatterCountStyleBinary in countStyle.

NSByteCountFormatterCountStyleFile: Specifies display of file or storage byte counts. The actual behavior for this is platform-specific; on OS X 10.8, this uses the decimal style, but that may change over time.

NSByteCountFormatterCountStyleMemory: Specifies display of memory byte counts. The actual behavior for this is platform-specific; on OS X 10.8, this uses the binary style, but that may change over time.

NSByteCountFormatterCountStyleDecimal: Specifies the number of bytes for KB explicitly, 1000 bytes are shown as 1 KB

NSByteCountFormatterCountStyleBinary: Specifies the number of bytes for KB explicitly, 1024 bytes are shown as 1 KB