fegetenv, fesetenv
来自 cppreference.com
| 在头文件 <fenv.h> 中定义 |
||
| int fegetenv( fenv_t* envp ); |
(1) | (自 C99 起) |
| int fesetenv( const fenv_t* envp ); |
(2) | (自 C99 起) |
1) 尝试将浮点环境的状态存储在 envp 指向的对象中。
2) 尝试从 envp 指向的对象中建立浮点环境。该对象的值必须先前通过调用 feholdexcept 或 fegetenv 获取，或者是一个浮点宏常量。如果 envp 中设置了任何浮点状态标志，它们将在环境中设置为已设置（并且可以通过 fetestexcept 进行测试），但不会引发相应的浮点异常（执行将继续不中断）
内容 |
[编辑] 参数
| envp | - | 指向 fenv_t 类型的对象的指针，该对象保存浮点环境的状态 |
[编辑] 返回值
0 成功时，否则为非零值。
[编辑] 示例
运行此代码
#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; }
输出
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
