C++恒定结构成员初始化

Question

我的班上有一个常数struct timespec成员。我该如何初始化它？

我得到的唯一一个疯狂的想法是派生自己的timespec并给它一个构造函数。

非常感谢！

#include <iostream> 

class Foo 
{ 
    private: 
     const timespec bar; 

    public: 
     Foo (void) : bar (1 , 1) 
     { 

     } 
}; 


int main() { 
    Foo foo;  
    return 0; 
} 

Compilation finished with errors: source.cpp: In constructor 'Foo::Foo()': source.cpp:9:36: error: no matching function for call to 'timespec::timespec(int, int)' source.cpp:9:36: note: candidates are: In file included from sched.h:34:0, from pthread.h:25, from /usr/lib/gcc/i686-pc-linux-gnu/4.7.2/../../../../include/c++/4.7.2/i686-pc-linux-gnu/bits/gthr-default.h:41, from /usr/lib/gcc/i686-pc-linux-gnu/4.7.2/../../../../include/c++/4.7.2/i686-pc-linux-gnu/bits/gthr.h:150, from /usr/lib/gcc/i686-pc-linux-gnu/4.7.2/../../../../include/c++/4.7.2/ext/atomicity.h:34, from /usr/lib/gcc/i686-pc-linux-gnu/4.7.2/../../../../include/c++/4.7.2/bits/ios_base.h:41, from /usr/lib/gcc/i686-pc-linux-gnu/4.7.2/../../../../include/c++/4.7.2/ios:43, from /usr/lib/gcc/i686-pc-linux-gnu/4.7.2/../../../../include/c++/4.7.2/ostream:40, from /usr/lib/gcc/i686-pc-linux-gnu/4.7.2/../../../../include/c++/4.7.2/iostream:40, from source.cpp:1: time.h:120:8: note: timespec::timespec() time.h:120:8: note: candidate expects 0 arguments, 2 provided time.h:120:8: note: constexpr timespec::timespec(const timespec&) time.h:120:8: note: candidate expects 1 argument, 2 provided time.h:120:8: note: constexpr timespec::timespec(timespec&&) time.h:120:8: note: candidate expects 1 argument, 2 provided

Answer 1

在C++ 11，你可以initalise在构造函数中的初始化器列表中的总成员：

Foo() : bar{1,1} {} 

在旧版本的语言，你需要一个工厂函数：

Foo() : bar(make_bar()) {} 

static timespec make_bar() {timespec bar = {1,1}; return bar;} 

Answer 2

使用初始化列表

class Foo 
{ 
    private: 
     const timespec bar; 

    public: 
     Foo (void) : 
      bar(100) 
     { 

     } 
}; 

如果你想与护腕初始化结构，然后用它们

Foo (void) : bar({1, 2}) 

Answer 3

使用带有一个辅助函数初始化列表：

#include <iostream> 
#include <time.h> 
#include <stdexcept> 

class Foo 
{ 
    private: 
     const timespec bar; 

    public: 
     Foo (void) : bar (build_a_timespec()) 
     { 

     } 
    timespec build_a_timespec() { 
     timespec t; 

     if(clock_gettime(CLOCK_REALTIME, &t)) { 
     throw std::runtime_error("clock_gettime"); 
     } 
     return t; 
    } 
}; 


int main() { 
    Foo foo;  
    return 0; 
}