FE_DFL_ENV
来自 cppreference.com
| 在头文件 <fenv.h> 中定义 |
||
| #define FE_DFL_ENV /*实现定义*/ |
(自 C99) | |
宏常量 FE_DFL_ENV 展开为类型 const fenv_t* 的表达式，它指向默认浮点环境的完整副本，即程序启动时加载的环境。
实现可能支持以 FE_ 后跟大写字母开头的其他宏，其类型为 const fenv_t*。
[编辑] 示例
运行此代码
#include <stdio.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() { printf("On startup:\n"); show_fe_environment(); // Change environment fesetround(FE_DOWNWARD); // change rounding mode feraiseexcept(FE_INVALID); // raise exception printf("\nBefore restoration:\n"); show_fe_environment(); fesetenv(FE_DFL_ENV); // restore printf("\nAfter restoring default environment:\n"); show_fe_environment(); }
输出
On startup: current exceptions raised: none current rounding method: FE_TONEAREST Before restoration: current exceptions raised: FE_INVALID current rounding method: FE_DOWNWARD After restoring default environment: current exceptions raised: none current rounding method: FE_TONEAREST
