ios float 和 double 有什么区别？
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What's the difference between float and double?
提问by saturngod
When I run the following code ,
当我运行以下代码时，
NSString* s= @"10000000.01";
float f = [s floatValue];
double d = [s doubleValue];
if(f > 10000000)
{
NSLog(@"Over Value");
}
else {
NSLog(@"OK Float");
}
if(d > 10000000)
{
NSLog(@"Over value");
}
else {
NSLog(@"OK Double");
}
The response is like following.
响应如下。
2013-04-19 17:07:29.284 float[2991:907] OK Float
2013-04-19 17:07:29.287 float[2991:907] Over value
Why float value changed to 10000000.00 instead of 10000000.01 ?
为什么浮点值改为 10000000.00 而不是 10000000.01 ？
回答by rmaddy
floatis 32-bit while doubleis 64-bit. A float has fewer significant digits than double.
float是 32 位，而double64 位。浮点数的有效数字少于双精度数。
A floatvalue doesn't store enough to hold the 10 digits of your 10000000.01.
一个float值不能存储足够的 10 位数字10000000.01。
Also see Difference between float and doublefor more details. That is about C/C++ but it applies to Objective-C as well.
另请参阅float 和 double 之间的差异以获取更多详细信息。那是关于 C/C++ 的，但它也适用于 Objective-C。
