C 将一个文字定义为另一个文字的倍数会导致错误的结果
为什么以下代码在分母中使用4*PI的文本时给出错误的结果,如C 将一个文字定义为另一个文字的倍数会导致错误的结果,c,literals,C,Literals,为什么以下代码在分母中使用4*PI的文本时给出错误的结果,如1.0/FOUR_PI #include <stdio.h> #define PI 3.14159265358979323846 #define FOUR_PI 4.0*PI int main() { printf("4.0*PI = %.20lf\n", 4.0*PI); printf("FOUR_PI = %.20lf\n", FOUR_PI); printf("4.0*PI - FOUR_PI =
1.0/FOUR_PI
#include <stdio.h>
#define PI 3.14159265358979323846
#define FOUR_PI 4.0*PI
int main() {
printf("4.0*PI = %.20lf\n", 4.0*PI);
printf("FOUR_PI = %.20lf\n", FOUR_PI);
printf("4.0*PI - FOUR_PI = %.60lf\n", 4.0*PI - FOUR_PI);
printf("1.0/(4.0*PI) = %.20lf\n", 1.0/(4.0*PI));
printf("1.0/FOUR_PI = %.20lf\n", 1.0/FOUR_PI);
return 0;
}
#包括
#定义PI 3.14159265358979323846
#定义四个_PI 4.0*PI
int main(){
printf(“4.0*PI=%.20lf\n”,4.0*PI);
printf(“四个圆周率=%.20lf\n”,四个圆周率);
printf(“4.0*PI-FOUR_-PI=%.60lf\n”,4.0*PI-FOUR_-PI);
printf(“1.0/(4.0*PI)=%.20lf\n”,1.0/(4.0*PI));
printf(“1.0/FOUR_PI=%.20lf\n”,1.0/FOUR_PI);
返回0;
}
结果表明,在解析文本时,它的表达式被替换为代码,而不是它的值。也就是说,1.0/FOUR_PI
正被1.0/4.0*PI
所取代。请参见以下示例进行说明:
#include <stdio.h>
#define PI 3.14159265358979323846
#define FOUR_PI (4.0*PI)
#define FOUR_PI2 4.0*PI
int main() {
printf("4.0*PI = %.20lf\n", 4.0*PI);
printf("FOUR_PI = %.20lf\n", FOUR_PI);
printf("FOUR_PI2 = %.20lf\n", FOUR_PI2);
printf("4.0*PI - FOUR_PI = %.20lf\n", 4.0*PI - FOUR_PI);
printf("4.0*PI - FOUR_PI2 = %.20lf\n", 4.0*PI - FOUR_PI2);
printf("1.0/(4.0*PI) = %.20lf\n", 1.0/(4.0*PI));
printf("1.0/FOUR_PI = %.20lf\n", 1.0/FOUR_PI);
printf("1.0/(FOUR_PI) = %.20lf\n", 1.0/(FOUR_PI));
printf("1.0/FOUR_PI2 = %.20lf\n", 1.0/FOUR_PI2);
return 0;
}
它的表达式被替换到代码中,而不是它的值。预处理器就是这样工作的,是的。括号是你的朋友
4.0*PI
不是文字
4.0*PI = 12.56637061435917246399
FOUR_PI = 12.56637061435917246399
FOUR_PI2 = 12.56637061435917246399
4.0*PI - FOUR_PI = 0.00000000000000000000
4.0*PI - FOUR_PI2 = 0.00000000000000000000
1.0/(4.0*PI) = 0.07957747154594767280
1.0/FOUR_PI = 0.07957747154594767280
1.0/(FOUR_PI) = 0.07957747154594767280
1.0/FOUR_PI2 = 0.78539816339744827900