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#2
lchydp2021-05-04 18:53
另外，上述文章中的宏FE_DIVBYZERO不知道什么时候能匹配到。如果除法的分母为0，是不能通过编译的，而分母是接近于0的数，也不能产生这个异常
 程序代码：#include <stdio.h> #include <math.h> #include <float.h> #include <fenv.h> #pragma STDC FENV_ACCESS ON void show_fe_exceptions(void) { int result; printf("exceptions raised:"); if (result = fetestexcept(FE_DIVBYZERO)) { printf(" FE_DIVBYZERO\n"); printf("result = %d\n", result); } else if (result = fetestexcept(FE_INEXACT)) { printf(" FE_INEXACT\n"); printf("result = %d\n", result); } else if (result = fetestexcept(FE_INVALID)) { printf(" FE_INVALID\n"); printf("result = %d\n", result); } else if (result = fetestexcept(FE_OVERFLOW)) { printf(" FE_OVERFLOW\n"); printf("result = %d\n", result); } else if (result = fetestexcept(FE_UNDERFLOW)) { printf(" FE_UNDERFLOW\n"); printf("result = %d\n", result); } else { printf(" no above expections\n"); printf("result = %d\n", result); } feclearexcept(FE_ALL_EXCEPT); printf("\n"); } int main(void) { printf("MATH_ERREXCEPT is %s\n\n", math_errhandling & MATH_ERREXCEPT ? "set" : "not set"); /*printf("0.0/0.0 = %f\n", 0.0 / 0.0);///< 编译不能通过，错误：C2124，被零除或对零求模 show_fe_exceptions(); printf("1.0/0.0 = %f\n", 1.0 / 0.0);///< 编译不能通过，错误：C2124，被零除或对零求模 show_fe_exceptions();*/ printf("0.0/DBL_MIN = %f\n", 0.0 / DBL_MIN);///< 未产生上述异常，0.0/DBL_MIN = 0.000000 show_fe_exceptions(); printf("0.0/(DBL_MIN * -1) = %f\n", 0.0 / (DBL_MIN * -1));///< 未产生上述异常，0.0/(DBL_MIN * -1) = -0.000000 show_fe_exceptions(); return 0; } [此贴子已经被作者于2021-5-4 18:54编辑过] |
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，按照这篇文章测试。如果运算产生了上溢和下溢，并未匹配到对应的宏。程序代码：#include <stdio.h>
#include <math.h>
#include <float.h>
#include <fenv.h>
#pragma STDC FENV_ACCESS ON
void show_fe_exceptions(void)
{
int result;
printf("exceptions raised:");
if (result = fetestexcept(FE_DIVBYZERO))
{
printf(" FE_DIVBYZERO\n");
printf("result = %d\n", result);
}
else if (result = fetestexcept(FE_INEXACT))
{
printf(" FE_INEXACT\n");
printf("result = %d\n", result);
}
else if (result = fetestexcept(FE_INVALID))
{
printf(" FE_INVALID\n");
printf("result = %d\n", result);
}
else if (result = fetestexcept(FE_OVERFLOW))
{
printf(" FE_OVERFLOW\n");
printf("result = %d\n", result);
}
else if (result = fetestexcept(FE_UNDERFLOW))
{
printf(" FE_UNDERFLOW\n");
printf("result = %d\n", result);
}
else
{
printf(" no above expections\n");
printf("result = %d\n", result);
}
feclearexcept(FE_ALL_EXCEPT);
printf("\n");
}
int main(void)
{
printf("MATH_ERREXCEPT is %s\n\n",
math_errhandling & MATH_ERREXCEPT ? "set" : "not set");
float toobig = 3.4E38 * 100.0f;
printf("toobig = %e\n", toobig);///< 未产生上述异常，输出inf
show_fe_exceptions();
float toosmall = 1.0 * 3.4E-65565;
printf("toosmall = %e\n", toosmall);///< 未产生上述异常，输出0.000000e+00
show_fe_exceptions();
return 0;
}
请问这是为什么呢？C语言检测计算产生subnormal值的函数究竟是哪个呢？
[此贴子已经被作者于2021-5-4 18:54编辑过]
