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

来自 cppreference.com
< cpp‎ | io‎ | basic ios
 
C++
 
输入/输出库
 
std::basic_ios
 
bool good() const;

如果流上最近的 I/O 操作成功完成，则返回 true。具体来说，返回 rdstate() == 0 的结果。

有关设置流状态位的条件列表，请参阅 ios_base::iostate。

内容

[编辑] 参数

(无)

[编辑] 返回值

如果流错误标志均为假，则返回 true，否则返回 false。

[编辑] 示例

运行此代码
#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";
}

可能的输出

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

[编辑] 另请参阅

下表显示了 basic_ios 访问器（good()、fail() 等）对于所有可能的 ios_base::iostate 标志组合的值

ios_base::iostate 标志 basic_ios 访问器
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
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