fegetenv, fesetenv
來自 cppreference.com
| 定義於標頭檔案 <fenv.h> |
||
| int fegetenv( fenv_t* envp ); |
(1) | (C99 起) |
| int fesetenv( const fenv_t* envp ); |
(2) | (C99 起) |
1) 嘗試將浮點環境的狀態儲存在 envp 指向的物件中。
2) 嘗試從 envp 指向的物件建立浮點環境。該物件的值必須以前透過呼叫 feholdexcept 或 fegetenv 或為浮點宏常量而獲得。如果 envp 中設定了任何浮點狀態標誌，它們將在環境中設定（然後可以透過 fetestexcept 進行測試），但不會引發相應的浮點異常（執行不中斷地繼續）。
目錄 |
[編輯] 引數
| envp | - | 指向型別為 fenv_t 的物件的指標，該物件儲存浮點環境的狀態 |
[編輯] 返回值
成功時返回 0，否則返回非零值。
[編輯] 示例
執行此程式碼
#include <stdio.h> #include <math.h> #include <fenv.h> #pragma STDC FENV_ACCESS ON void show_fe_exceptions(void) { printf("current exceptions raised: "); if(fetestexcept(FE_DIVBYZERO)) printf(" FE_DIVBYZERO"); if(fetestexcept(FE_INEXACT)) printf(" FE_INEXACT"); if(fetestexcept(FE_INVALID)) printf(" FE_INVALID"); if(fetestexcept(FE_OVERFLOW)) printf(" FE_OVERFLOW"); if(fetestexcept(FE_UNDERFLOW)) printf(" FE_UNDERFLOW"); if(fetestexcept(FE_ALL_EXCEPT)==0) printf(" none"); printf("\n"); } void show_fe_rounding_method(void) { printf("current rounding method: "); switch (fegetround()) { case FE_TONEAREST: printf ("FE_TONEAREST"); break; case FE_DOWNWARD: printf ("FE_DOWNWARD"); break; case FE_UPWARD: printf ("FE_UPWARD"); break; case FE_TOWARDZERO: printf ("FE_TOWARDZERO"); break; default: printf ("unknown"); }; printf("\n"); } void show_fe_environment(void) { show_fe_exceptions(); show_fe_rounding_method(); } int main(void) { fenv_t curr_env; int rtn; /* Show default environment. */ show_fe_environment(); printf("\n"); /* Perform some computation under default environment. */ printf("+11.5 -> %+4.1f\n", rint(+11.5)); /* midway between two integers */ printf("+12.5 -> %+4.1f\n", rint(+12.5)); /* midway between two integers */ show_fe_environment(); printf("\n"); /* Save current environment. */ rtn = fegetenv(&curr_env); /* Perform some computation with new rounding method. */ feclearexcept(FE_ALL_EXCEPT); fesetround(FE_DOWNWARD); printf("1.0/0.0 = %f\n", 1.0/0.0); printf("+11.5 -> %+4.1f\n", rint(+11.5)); printf("+12.5 -> %+4.1f\n", rint(+12.5)); show_fe_environment(); printf("\n"); /* Restore previous environment. */ rtn = fesetenv(&curr_env); show_fe_environment(); return 0; }
輸出
current exceptions raised: none current rounding method: FE_TONEAREST +11.5 -> +12.0 +12.5 -> +12.0 current exceptions raised: FE_INEXACT current rounding method: FE_TONEAREST 1.0/0.0 = inf +11.5 -> +11.0 +12.5 -> +12.0 current exceptions raised: FE_DIVBYZERO FE_INEXACT current rounding method: FE_DOWNWARD current exceptions raised: FE_INEXACT current rounding method: FE_TONEAREST
