map(value, fromLow, fromHigh, toLow, toHigh)
Description
Re-maps a number from one range to another. That is, a value of
fromLow would get mapped to toLow, a value of fromHigh to toHigh,
values in-between to values in-between, etc.
把一个数从一个范围变换到另一个范围。
Does not constrain values to within the range, because out-of-range
values are sometimes intended and useful. The constrain() function
may be used either before or after this function, if limits to the
ranges are desired.
不会把值强制限制在范围之内，因为超范围的值经常也是有用的。如果需要的范围做一限制。可以在这个函数之前或之后使用constrain()
函数。
Note that the "lower bounds" of either range may be larger or
smaller than the "upper bounds" so the map() function may be used
to reverse a range of numbers, for example
注意，两个范围中的“下界”要比“上界”大或下，这样map（）可以用来反转一个范围，例如
y = map(x, 1, 50, 50, 1);
The function also handles negative numbers well, so that this
example
函数也可以处理负数，例如
y = map(x, 1, 50, 50, -100);
is also valid and works well.
也有效和正确
The map() function uses integer math so will not generate
fractions, when the math might indicate that it should do so.
Fractional remainders are truncated, and are not rounded or
averaged.
map（）函数使用整型，所以不会产生分数，分数将会被截去，并不是全面的或平均值（？）
Parameters 参数
value: the number to map
给map的值
fromLow: the lower bound of the value‘s current range
值现在的下界
fromHigh: the upper bound of the value‘s current range
值现在的上界
toLow: the lower bound of the value‘s target range
值目标范围的下界
toHigh: the upper bound of the value‘s target range
值目标范围的上界
Returns 返回值
The mapped value.
映射的值
Example
void setup() {}
void loop()
{
int val = analogRead(0); //读取0口的值
val = map(val, 0, 1023, 0, 255);//从0-1023映射到0-255
analogWrite(9, val);//把映射后的值写给9口
}
Appendix 附录
For the mathematically inclined, here‘s the whole function
对于数学上来说,这是整个函数
long map(long x, long in_min, long in_max, long out_min, long
out_max)
{
return (x - in_min) * (out_max - out_min) / (in_max - in_min) +
out_min;
}