std::basic_ios<CharT,Traits>::good

 

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std::basic_ios

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bool good() const;

如果流上最近的 I/O 操作成功完成，則返回 true。具體來說，返回 rdstate() == 0 的結果。

有關設定流狀態位的條件列表，請參閱 ios_base::iostate。

引數

(無)

返回值

如果所有流錯誤標誌都為 false，則為 true，否則為 false。

示例

執行此程式碼

#include <cstdlib>
#include <fstream>
#include <iostream>
 
int main()
{
    const char* fname = "/tmp/test.txt";
    std::ofstream ofile{fname};
    ofile << "10 " << "11 " << "12 " << "non-int";
    ofile.close();
 
    std::ifstream file{fname};
    if (!file.good())  
    {  
        std::cout << "#1. Opening file test.txt failed - "
                     "one of the error flags is true\n";
        return EXIT_FAILURE;
    }
 
    // typical C++ I/O loop uses the return value of the I/O function
    // as the loop controlling condition, operator bool() is used here
    for (int n; file >> n;)
        std::cout << n << ' ';
    std::cout << '\n';
 
    if (file.bad()) 
    {
        std::cout << "#2. I/O error while reading - badbit is true\n";
        return EXIT_FAILURE;
    } 
    else if (file.eof())
        std::cout << "#3. End of file reached successfully - eofbit is true\n"
            "This is fine even though file.good() is false\n"; 
    else if (file.fail())
        std::cout << "#4. Non-integer data encountered - failbit is true\n";
}

可能的輸出

10 11 12 
#4. Non-integer data encountered - failbit is true

另請參閱

下表顯示了在 ios_base::iostate 標誌所有可能組合下 basic_ios 訪問器（good()、fail() 等）的值

ios_base::iostate 標誌			basic_ios 訪問器
eofbit	failbit	badbit	good()	fail()	bad()	eof()	operator bool	operator!
false	false	false	true	false	false	false	true	false
false	false	true	false	true	true	false	false	true
false	true	false	false	true	false	false	false	true
false	true	true	false	true	true	false	false	true
true	false	false	false	false	false	true	true	false
true	false	true	false	true	true	true	false	true
true	true	false	false	true	false	true	false	true
true	true	true	false	true	true	true	false	true