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在头文件<fenv.h>中定义 | ||
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int feupdateenv(const fenv_t * envp); | (自C99以来) |
首先,记住当前浮点异常,然后从envp指向的对象(类似于fesetenv)恢复浮点环境,然后引发已保存的浮点异常。
这个功能可以用来结束早期调用feholdexcept所建立的不间断模式。
envp | - | pointer to the object of type fenv_t set by an earlier call to feholdexcept or fegetenv or equal to FE_DFL_ENV |
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成功时为0,否则为非零。
#include <stdio.h>#include <fenv.h>#include <float.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");} double x2 (double x) /* times two */{ fenv_t curr_excepts; /* Save and clear current f-p environment. */ feholdexcept(&curr_excepts); /* Raise inexact and overflow exceptions. */ printf("In x2(): x = %f\n", x=x*2.0); show_fe_exceptions(); feclearexcept(FE_INEXACT); /* hide inexact exception from caller */ /* Merge caller's exceptions (FE_INVALID) */ /* with remaining x2's exceptions (FE_OVERFLOW). */ feupdateenv(&curr_excepts); return x;} int main(void){ feclearexcept(FE_ALL_EXCEPT); feraiseexcept(FE_INVALID); /* some computation with invalid argument */ show_fe_exceptions(); printf("x2(DBL_MAX) = %f\n", x2(DBL_MAX)); show_fe_exceptions(); return 0;}
输出:
current exceptions raised: FE_INVALID In x2(): x = inf current exceptions raised: FE_INEXACT FE_OVERFLOWx2(DBL_MAX) = inf current exceptions raised: FE_INVALID FE_OVERFLOW
C11标准(ISO / IEC 9899:2011):
7.6.4.4 feupdateenv函数(p:214-215)
C99标准(ISO / IEC 9899:1999):
7.6.4.4 feupdateenv函数(p:195-196)
feholdexcept(C99) | 保存环境,清除所有状态标志并忽略所有将来的错误(功能) |
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fegetenvfesetenv(C99) | 保存或恢复当前的浮点环境(功能) |
FE_DFL_ENV(C99) | 默认浮点环境(宏常量) |
| feupdateenv的C ++文档 |