取整函數：

ceil()?????右向取整：數軸上右邊最靠近的整數，向大的方向取值；ceil “天花板”
floor()???左向取整：數軸上左邊最靠近的整數，向小的方向取值；floor “地板”
round() 接近取整：不管正負，即四舍五入后留下整數部分??round(x) = floor(x+0.5)
trunc()??零向取整：不管正負，直接舍掉小數部分只留下整數部分，向原點0的方向取值
rint() nearbyint()：四種方法任選其一，由?fesetround()?配合設置，見例程二說明

例程一：ceil() floor() round() trunc()用法

#include <iostream> #include <cmath>using namespace std;int main() {double num[4] = {13.6, 3.23, -13.6, -3.23};for (auto n:num){cout<< " ceil(x) floor(x) round(x) trunc(x)：x = " << n << endl;cout<< "\t" << ceil(n) << "\t" << floor(n) << "\t"<< round(n) << "\t" << trunc(n) << endl << endl;}return 0; }/*ceil(x) floor(x) round(x) trunc(x)：x = 13.614 13 14 13ceil(x) floor(x) round(x) trunc(x)：x = 3.234 3 3 3ceil(x) floor(x) round(x) trunc(x)：x = -13.6-13 -14 -14 -13ceil(x) floor(x) round(x) trunc(x)：x = -3.23-3 -4 -3 -3-------------------------------- Process exited after 0.6186 seconds with return value 0 請按任意鍵繼續. . . */

例程二：fegetround() fesetround()用法

函數原型：
int fesetround(int mode); 設置取整模式
int fegetround(void); 獲取當前取整模式

mode 值：
Round to nearest value ? FE_TONEAREST? ? ?== 0
Round downward? ? ? ? ? ? FE_DOWNWARD? ? ?== 1024
Round upward? ? ? ? ? ? ? ? ?FE_UPWARD? ? ? ? ? ?== 2048
Round towards zero? ? ? ? FE_TOWARDZERO ?== 3072
default value：? ? ? ? ? ? ?? ?FE_TONEAREST? ? ? == 0

#include <iostream> #include <cmath> #include <cfenv> using namespace std;int getround(void) {switch (fegetround()) { case FE_TONEAREST:cout << "\nRound to nearest value \t FE_TONEAREST\t== "; break; //round()case FE_DOWNWARD:cout << "\nRound downward \t\t FE_DOWNWARD\t== "; break; //ceil()case FE_UPWARD:cout << "\nRound upward \t\t FE_UPWARD\t== "; break; //floor()case FE_TOWARDZERO:cout << "\nRound towards zero \t FE_TOWARDZERO\t== "; break; //trunc()default: cout << "unknown";}return fegetround(); }int main(void) {for(int i=0;i<4;i++){fesetround(i*1024);cout << getround();}cout << "\n\nDaufult: TONEAREST == 0" << endl; return 0; }/*Round to nearest value FE_TONEAREST == 0 Round downward FE_DOWNWARD == 1024 Round upward FE_UPWARD == 2048 Round towards zero FE_TOWARDZERO == 3072Daufult: TONEAREST == 0-------------------------------- Process exited after 0.8902 seconds with return value 0 請按任意鍵繼續. . . */

例程三：nearbyint() rint()用法

#include <iostream> #include <array> #include <cmath> #include <cfenv> using namespace std;int main(void) {array<double,4> num={13.6, 3.23, -13.6, -3.23};array<string,6> str={"nearbyint(x), x = \n", "\nmode = ","FE_TONEAREST(default) = ","FE_DOWNWARD = ","FE_UPWARD = ","FE_TOWARDZERO = " };cout<<str.at(0);for (auto n:num) cout<<"\t"<<n; cout<<endl;for (int i=0;i<4;i++){fesetround(i*1024);cout<<str.at(1)<<str.at(i+2)<<fegetround()<<endl;for (auto n:num) cout<<"\t"<<nearbyint(n); cout<<endl;}return 0; }/* nearbyint(x), x =13.6 3.23 -13.6 -3.23mode = FE_TONEAREST(default) = 014 3 -14 -3mode = FE_DOWNWARD = 102413 3 -14 -4mode = FE_UPWARD = 204814 4 -13 -3mode = FE_TOWARDZERO = 307213 3 -13 -3-------------------------------- Process exited after 0.6 seconds with return value 0 請按任意鍵繼續. . . */

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