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

From cppreference.net
C++
Input/output library
std::basic_ios
bool good ( ) const ;

若流上的最近一次I/O操作成功完成则返回 true 。具体而言，返回 rdstate ( ) == 0 的结果。

请参阅 ios_base::iostate 了解设置流状态位的条件列表。

目录

参数

(无)

返回值

true 表示流错误标志位均为 false， false 则表示其他情况。

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

参见

以下表格展示了所有可能的 ios_base::iostate 标志组合下， basic_ios 访问器（ good() 、 fail() 等）的对应值：

ios_base::iostate 标志位 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