为什么不显式调用构造函数呢？boost::optional<std::string> my_optional_string("hello");...
std::string s = argv[1] ; char t = *argv[2] ; boost::optional<int> idx = find (s, t) ; if (idx) std::cout << "found at " << *idx << std::endl ; else std::cout << "not found" << std::endl ; return 0 ; } 本质上 optional 只是额外维护了一个 bool 标志是否初始...
For example, the member function find() of the class std::string returns the special value std::string::npos if a substring can’t be found. Functions whose return value is a pointer often return 0 to indicate that no result exists....
1:#include <string> 2:#include <iostream> 3:#include <boost/optional.hpp> 4: 5:using namespace std; 6:struct T { 7:string str; 8:bool flag; 9: 10:T(string s, bool f) { 11:str = s; 12:flag = f; 13:} 14:}; 15: 16:boost::optional<T> test(bool flag)const{ 17:boos...
#include <string> #include "boost/optional.hpp" #include "boost/variant.hpp" using namespace std; deque<char> queue; // //char get_async_data() { // if (!queue.empty()) // return queue.back(); // else // return '\0'; // 空的时候返回什么?返回'\0'是一个非法的字符 //} ...
问如何使用boost::optionalENC++ 17 引入了std::optional，表示一个可能有值的对象（没有值时就是默认...
return std::nullopt; } private: status do_handle_401(const http_response_info&); boost::optional<std::pair<std::string, std::string>> do_get_auth_field(std::string_view, std::string_view); std::optional<std::pair<std::string, std::string>> do_get_auth_field(std::string_view, ...
add_configs("std", {description="Choose C++ standard version.",default="cxx17",type="string",values={"cxx98","cxx11","cxx14","cxx17","cxx20"}}) add_configs("boost", {description="Use Boost",default=is_plat("macosx","linux","windows","bsd","mingw","cross"),type="boolean"})...
#include<boost/optional.hpp>using namespace boost;using namespace std;intmain(){optional<int>op0;//一个未初始化的optional对象optional<int>op1(boost::none);//同上,使用none赋予未初始化值assert(!op0);assert(op0==op1);assert(op1.get_value_or(253)==253);//获取可选值optional<string>ops(...
<iostream>#include<string>usingstd::cout;usingstd::endl;usingstd::string;#include<cstdlib>structMyStruct{MyStruct(){}MyStruct(inta,intb):m_a(a),m_b(b){}intm_a;intm_b;};voidtestOp(){Optional<string>a("ok");Optional<string>b("cancel");Optional<string>c("aa");Optional<string>d...