convering hex to rgb result in white

Question

I have this code for color converting :

// takes @"#123456"
+ (UIColor *)colorWithHexString:(NSString *)str {
    const char *cStr = [str cStringUsingEncoding:NSASCIIStringEncoding];
    long x = strtol(cStr+1, NULL, 16);
    return [UIColor colorWithHex:(UInt32)x];
}

// takes 0x123456
+ (UIColor *)colorWithHex:(UInt32)col {
    unsigned char r, g, b, a;
    b = col & 0xFF;
    g = (col >> 8) & 0xFF;
    r = (col >> 16) & 0xFF;
    a = (col >> 24) & 0xFF;
    if (a == 0) {
        a = 255.0;
    }
    return [UIColor colorWithRed:(float)r/255.0f green:(float)g/255.0f blue:(float)b/255.0f alpha:(float)a/255.0f];
}

The issue is when I test this code on the simulator return the right color, but when I test this on device (iPad mini 1) the color return

UIDeviceRGBColorSpace 1 1 1 0.0156863

which is white!

Answer 1

The iPad mini 1 has a 32-bit CPU, and the type long is a 32-bit signed integer.

The number 0xffdd6858 overflows the 32-bit signed integer range, and thus will return the maximum number 0x7fffffff instead, which is a translucent white.

To fix this, use strtoul to ensure we have at least an unsigned 32-bit integer:

unsigned long x = strtoul(cStr+1, NULL, 16);

The code is fine on the simulator since your computer should be a 64-bit CPU and long is a 64-bit signed integer, thus the strtol call doesn't overflow and keeps the actual value.

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Instead of writing your own method, consider reusing existing libraries like mRs-/HexColors or tinymind/UIColor-HexRGB.