宏定义

#define M_PI 3.1415926535
double r = 1.0;
double circlePerimeter = 2 * M_PI * r;
// => double circlePerimeter = 2 * 3.1415926535 * r ## 函数宏
#define FUNC(x) x
NSLog(@"Hello %@", FUNC("world");
// => NSLog(@"Hello %@", "world");