C++ fegetenv()用法及代碼示例

在頭文件cfenv.h中指定了C /C++中的fegetenv()函數，並嘗試將浮點環境的當前狀態存儲在envp指向的對象中。浮點環境是一組狀態標誌和控製模式，包括浮點異常和舍入方向模式。

用法:

int fegetenv( fenv_t* envp )

參數：該函數接受一個強製性參數envp，該參數指定一個對象，該對象存儲浮點環境的狀態。

返回值：該函數返回兩個值，如下所示：

成功時，它返回零。
失敗時，它返回非零。

以下示例程序旨在說明上述函數：
程序1:

// C++ program to illustrate 
// fegetenv() function 
  
#include <bits/stdc++.h> 
using namespace std; 
  
// rounding direction mode 
void rounding_mode() 
{ 
    cout << "Rounding mode is ->"; 
    switch (fegetround()) { 
    case FE_TONEAREST:
  
        // Round to nearest 
        cout << "FE_TONEAREST" << endl; 
        break; 
    case FE_DOWNWARD:
  
        // Round downward 
        cout << "FE_DOWNWARD" << endl; 
        break; 
    case FE_UPWARD:
  
        // Round upward 
        cout << "FE_UPWARD" << endl; 
        break; 
    case FE_TOWARDZERO:
  
        // Round toward zero 
        cout << "FE_TOWARDZERO" << endl; 
        break; 
    default:
        cout << "unknown" << endl; 
    }; 
} 
  
int main(void) 
{ 
    fenv_t envp; 
  
    // initial environment 
    cout << "Initial environment:" << endl; 
  
    // print the exception raised initially 
    cout << "Exception raised -> \n"; 
    if (fetestexcept(FE_ALL_EXCEPT)) { 
        if (fetestexcept(FE_DIVBYZERO)) 
            cout << "FE_DIVBYZERO " << endl; 
        if (fetestexcept(FE_INEXACT)) 
            cout << "FE_INEXACT " << endl; 
        if (fetestexcept(FE_INVALID)) 
            cout << "FE_INVALID " << endl; 
        if (fetestexcept(FE_OVERFLOW)) 
            cout << "FE_OVERFLOW " << endl; 
        if (fetestexcept(FE_UNDERFLOW)) 
            cout << "FE_UNDERFLOW " << endl; 
    } 
    else
        cout << "None" << endl; 
  
    // print the rounding direction mode 
    rounding_mode(); 
  
    // Current environment 
    fegetenv(&envp); 
    feraiseexcept(FE_INVALID); 
  
    // Set rounding direction mode 
    fesetround(FE_DOWNWARD); 
  
    // after environment is change 
    cout << endl 
         << "Final environment:" << endl; 
  
    // print the exception raised 
    cout << "Exception raised -> \n"; 
    if (fetestexcept(FE_ALL_EXCEPT)) { 
        if (fetestexcept(FE_DIVBYZERO)) 
            cout << "FE_DIVBYZERO " << endl; 
        if (fetestexcept(FE_INEXACT)) 
            cout << "FE_INEXACT " << endl; 
        if (fetestexcept(FE_INVALID)) 
            cout << "FE_INVALID " << endl; 
        if (fetestexcept(FE_OVERFLOW)) 
            cout << "FE_OVERFLOW " << endl; 
        if (fetestexcept(FE_UNDERFLOW)) 
            cout << "FE_UNDERFLOW " << endl; 
    } 
    else
        cout << "None" << endl; 
  
    // print the rounding direction mode 
    rounding_mode(); 
  
    return 0; 
}

輸出：

Initial environment:
Exception raised -> 
None
Rounding mode is ->FE_TONEAREST

Final environment:
Exception raised -> 
FE_INVALID 
Rounding mode is ->FE_DOWNWARD

程序2:

// C++ program to illustrate 
// fegetenv() function 
  
#include <bits/stdc++.h> 
using namespace std; 
  
// rounding direction mode 
void rounding_mode() 
{ 
    cout << "Rounding mode is ->"; 
    switch (fegetround()) { 
    case FE_TONEAREST:
  
        // Round to nearest 
        cout << "FE_TONEAREST" << endl; 
        break; 
    case FE_DOWNWARD:
  
        // Round downward 
        cout << "FE_DOWNWARD" << endl; 
        break; 
    case FE_UPWARD:
  
        // Round upward 
        cout << "FE_UPWARD" << endl; 
        break; 
    case FE_TOWARDZERO:
  
        // Round toward zero 
        cout << "FE_TOWARDZERO" << endl; 
        break; 
    default:
        cout << "unknown" << endl; 
    }; 
} 
  
int main(void) 
{ 
    fenv_t envp; 
  
    // initial environment 
    cout << "Initial environment:" << endl; 
  
    // print the exception raised initially 
    cout << "Exception raised -> \n"; 
    if (fetestexcept(FE_ALL_EXCEPT)) { 
        if (fetestexcept(FE_DIVBYZERO)) 
            cout << "FE_DIVBYZERO " << endl; 
        if (fetestexcept(FE_INEXACT)) 
            cout << "FE_INEXACT " << endl; 
        if (fetestexcept(FE_INVALID)) 
            cout << "FE_INVALID " << endl; 
        if (fetestexcept(FE_OVERFLOW)) 
            cout << "FE_OVERFLOW " << endl; 
        if (fetestexcept(FE_UNDERFLOW)) 
            cout << "FE_UNDERFLOW " << endl; 
    } 
    else
        cout << "None" << endl; 
  
    // print the rounding direction mode 
    rounding_mode(); 
  
    // Current environment 
    fegetenv(&envp); 
    feraiseexcept(FE_ALL_EXCEPT); 
  
    // Set rounding direction mode 
    fesetround(FE_DOWNWARD); 
  
    // after environment is change 
    cout << endl 
         << "Final environment:" << endl; 
  
    // print the exception raised 
    cout << "Exception raised -> \n"; 
    if (fetestexcept(FE_ALL_EXCEPT)) { 
        if (fetestexcept(FE_DIVBYZERO)) 
            cout << "FE_DIVBYZERO " << endl; 
        if (fetestexcept(FE_INEXACT)) 
            cout << "FE_INEXACT " << endl; 
        if (fetestexcept(FE_INVALID)) 
            cout << "FE_INVALID " << endl; 
        if (fetestexcept(FE_OVERFLOW)) 
            cout << "FE_OVERFLOW " << endl; 
        if (fetestexcept(FE_UNDERFLOW)) 
            cout << "FE_UNDERFLOW " << endl; 
    } 
    else
        cout << "None" << endl; 
  
    // print the rounding direction mode 
    rounding_mode(); 
  
    return 0; 
}

輸出：

Initial environment:
Exception raised -> 
None
Rounding mode is ->FE_TONEAREST

Final environment:
Exception raised -> 
FE_DIVBYZERO 
FE_INEXACT 
FE_INVALID 
FE_OVERFLOW 
FE_UNDERFLOW 
Rounding mode is ->FE_DOWNWARD

相關用法

注：本文由純淨天空篩選整理自AmanSrivastava1大神的英文原創作品 fegetenv() function in C/C++。非經特殊聲明，原始代碼版權歸原作者所有，本譯文未經允許或授權，請勿轉載或複製。