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在頭文件<fenv.h>中定義 | ||
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int fegetenv(fenv_t * envp); | (1) | (自C99以來) |
int fesetenv(const fenv_t * envp); | (2) | (自C99以來) |
1)試圖將浮點(diǎn)環(huán)境的狀態(tài)存儲(chǔ)在envp指向的對(duì)象中。
2)嘗試從envp指向的對(duì)象中建立浮點(diǎn)環(huán)境。 該對(duì)象的值必須事先通過調(diào)用feholdexcept或fegetenv獲得,或者是浮點(diǎn)宏常量。 如果在envp中設(shè)置了任何浮點(diǎn)狀態(tài)標(biāo)志,它們將在環(huán)境中設(shè)置(然后可用fetestexcept進(jìn)行測(cè)試),但不會(huì)引發(fā)相應(yīng)的浮點(diǎn)異常(執(zhí)行繼續(xù)不間斷)。
envp | - | pointer to the object of type fenv_t which holds the status of the floating-point environment |
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成功時(shí)為0,否則為非零。
#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 -> +12.0current exceptions raised: FE_INEXACT current rounding method: FE_TONEAREST 1.0/0.0 = inf+11.5 -> +11.0+12.5 -> +12.0current exceptions raised: FE_DIVBYZERO FE_INEXACT current rounding method: FE_DOWNWARD current exceptions raised: FE_INEXACT current rounding method: FE_TONEAREST
C11標(biāo)準(zhǔn)(ISO / IEC 9899:2011):
7.6.4.1 fegetenv函數(shù)(p:213)
7.6.4.3 fesetenv函數(shù)(p:214)
C99標(biāo)準(zhǔn)(ISO / IEC 9899:1999):
7.6.4.1 fegetenv函數(shù)(p:194)
7.6.4.3 fesetenv函數(shù)(p:195)
feholdexcept(C99) | 保存環(huán)境,清除所有狀態(tài)標(biāo)志并忽略所有將來的錯(cuò)誤(功能) |
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feupdateenv(C99) | 恢復(fù)浮點(diǎn)環(huán)境并引發(fā)以前引發(fā)的異常(函數(shù)) |
FE_DFL_ENV(C99) | 默認(rèn)浮點(diǎn)環(huán)境(宏常量) |
| fegetenv,fesetenv的C ++文檔 |