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insert vs emplace vs operator[] in c++ map

...itialization of one object and the copy of the value into that object. In C++11, with variadic templates and perfect forwarding there is a new way of adding elements into a container by means of emplacing (creating in place). The emplace functions in the different containers do basically the same t...
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Why isn't vector a STL container?

... For space-optimization reasons, the C++ standard (as far back as C++98) explicitly calls out vector<bool> as a special standard container where each bool uses only one bit of space rather than one byte as a normal bool would (implementing a kind of "dynam...
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What are forward declarations in C++?

... Why forward-declare is necessary in C++ The compiler wants to ensure you haven't made spelling mistakes or passed the wrong number of arguments to the function. So, it insists that it first sees a declaration of 'add' (or any other types, classes or functions)...
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Size of Matrix OpenCV

...of rows in a 2D array. mat.cols – Number of columns in a 2D array. Or: C++: Size Mat::size() const The method returns a matrix size: Size(cols, rows) . When the matrix is more than 2-dimensional, the returned size is (-1, -1). For multidimensional matrix, you need to use int thisSizes[3] = {...
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iPhone App 开发第一步:从零到真机调试HelloWorld - 更多技术 - 清泛网 - ...

...明出处! 最近才开始研究iPhone开发,由于没有Mac,采用是AMD CPU + Win7 + VMWare之后安装Mac OS X Snow Le... iCc原创,转载请注明出处! 最近才开始研究iPhone开发,由于没有Mac,采用是AMD CPU + Win7 + VMWare之后安装Mac OS X Snow Leopard,...
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What is the most effective way for float and double comparison?

...re function to sort items in a collection. (In this case using the builtin C++ operator == for doubles produced correct results.) Like I said: it all depends on context and the expected size of a and b. BTW, std::numeric_limits<double>::epsilon() is the "machine epsilon". It is the differen...
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How to automatically generate a stacktrace when my program crashes

I am working on Linux with the GCC compiler. When my C++ program crashes I would like it to automatically generate a stacktrace. ...
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error LNK2019: 无法解析外部符号_socket,该符号在函数 中被引用 - C/C+...

error LNK2019: 无法解析外部符号_socket,该符号在函数 中被引用1>NetClient.obj : error LNK2019: 无法解析外部符号 _closesocket@4,该符号在函数 _main 中被引用1>NetClient.obj : error L...1>NetClient.obj : error LNK2019: 无法解析外部符号 _closesocket@...
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CSingleLock类介绍 - C/C++ - 清泛网 - 专注C/C++及内核技术

...y aa313863(v=vs.60).aspxCSingleLockCSingleLock没有父类。类CSingleLock对象表示在控制...译自:https://msdn.microsoft.com/en-us/library/aa313863(v=vs.60).aspx CSingleLock CSingleLock 没有父类。 CSingleLock对象用于多线程程序中资源控制访问上。为使用...
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MFC中通过Tooltip类实现悬浮鼠标显示提示信息 - C/C++ - 清泛网 - 专注C/C++及内核技术

...现悬浮鼠标显示提示信息方法一:利用CWnd本身自身支持tooptip来实现,这种方法适用给控件增加tooltip,非常方便和简单方法如下:1、在窗口中增加消息映射ON_NOTI...方法一: 利用CWnd本身自身支持tooptip来实现,这种方法适用...