我想检查一个类中的变量是否已设置？我该怎么做？
enum Color {
red,
blue
};
class example {
Color c;
void set_color(Color c) { this->c = c; }
Color get_color() { return c; }
bool check_color_is_set() {
if (c == Color) {} // compile error
if (c == NULL) {} // compile error
return true;
}
我想知道变量是否Color c已分配？
我本来打算通过实施seekpos在流缓冲的GNU在线文档源.我无法理解为什么__mode在行中注释ios_base::openmode /*__mode*/ = ios_base::in | ios_base::out以及它为什么不抛出错误.
virtual pos_type
seekpos(pos_type, ios_base::openmode /*__mode*/ = ios_base::in | ios_base::out)
{
return pos_type(off_type(-1));
}
我可以理解评论的用法,如果它是以下格式:
void foo( pos_type, int /*blah*/ ){
...
}
但是,在前一种情况下,还有意图分配一些东西__mode,因此我很惊讶没有在那里得到任何错误.
这是允许的吗？如果是,那为什么呢？
我正在尝试使用tiny_obj_loader将其加载.obj到我的程序中。我有以下使用该库的代码：
void LoadModel(vector<Shape *> &scene, const char *path) {
attrib_t attrib;
vector<shape_t> shapes;
vector<material_t> materials;
std::string error;
bool ret = tinyobj::LoadObj(
&attrib,
&shapes,
&materials,
&error,
path
);
... // Do stuff with the returned data
然而，这给了我以下链接器错误：
Build/skeleton.o: In function `LoadModel(std::vector<Shape*,
std::allocator<Shape*> >&, char const*)':
skeleton.cpp:(.text+0x3025): undefined reference to `tinyobj::LoadObj(tinyobj::attrib_t*, std::vector<tinyobj::shape_t, std::allocator<tinyobj::shape_t> >*, std::vector<tinyobj::material_t, std::allocator<tinyobj::material_t> >*, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >*, char const*, char const*, bool)'
Makefile:43: recipe for target 'Build' failed
make: *** [Build] Error 1
其中函数定义是： …
我试图使用OpenCV编写一个简单的代码,但我无法成功编译它.以下是代码:
#include <iostream>
#include <stdio.h>
#include "opencv2/core/core.hpp"
#include "opencv2/highgui/highgui.hpp"
#include "opencv2/imgproc/imgproc.hpp"
using namespace std;
using namespace cv;
int main()
{
Mat img = imread("insignia.jpg", -1);
return 0;
}
它不会起作用.以下是我收到的错误消息.
/tmp/ccEMHPHa.o: In function `main':
main.cpp:(.text+0x46): undefined reference to `cv::imread(cv::String const&, int)'
/tmp/ccEMHPHa.o: In function `cv::String::String(char const*)':
main.cpp:(.text._ZN2cv6StringC2EPKc[_ZN2cv6StringC5EPKc]+0x58): undefined reference to `cv::String::allocate(unsigned long)'
/tmp/ccEMHPHa.o: In function `cv::String::~String()':
main.cpp:(.text._ZN2cv6StringD2Ev[_ZN2cv6StringD5Ev]+0x14): undefined reference to `cv::String::deallocate()'
/tmp/ccEMHPHa.o: In function `cv::Mat::~Mat()':
main.cpp:(.text._ZN2cv3MatD2Ev[_ZN2cv3MatD5Ev]+0x39): undefined reference to `cv::fastFree(void*)'
/tmp/ccEMHPHa.o: In function `cv::Mat::release()':
main.cpp:(.text._ZN2cv3Mat7releaseEv[_ZN2cv3Mat7releaseEv]+0x4b): undefined reference to `cv::Mat::deallocate()'
collect2: error: …我是C++的新手,两周前我开始用C++学习编码.为什么我的代码在构建和运行时总是给我结果0？请帮忙
# include <iostream>
# include <string>
using namespace std;
int main ()
{
int input = 1;
cout << "input your number : \n";
cin >> input;
int faktorial = 1;
for(int i=1;i<=input;i++)
{
faktorial = faktorial * i;
}
cout << "factorial value from number " << input << " is " << faktorial << endl;
}
我有一个课程如下:
handler.h中:
#ifndef HANDLER_H
#define HANDLER_H
#include <QObject>
class handler : public QObject
{
Q_OBJECT
public:
explicit handler(QObject *parent = nullptr);
~handler();
public slots:
void returnHandler(int input);
};
#endif // HANDLER_H
handler.cpp:
#include "handler.h"
#include "otherclass.h"
handler::handler(QObject *parent) : QObject(parent)
{
}
handler::~handler()
{
}
void handler::returnHandler(int input)
{
otherclass *otherclassPointer = otherclass::getInstance();
otherclassPointer->returnFunction(input);
}
如图所示,这是一个非常简单的类,旨在接收输入并将输入传递给外部类('otherclass')中的函数.在我的主应用程序('main.cpp')中,我创建了一个QThread,并returnHandler在QThread启动时调用插槽,如下所示:
main.cpp中:
QThread* newThread = new QThread();
handler* handlerPointer = new handler();
handlerPointer->moveToThread(newThread);
connect(newThread, SIGNAL(started()), handlerPointer, SLOT(returnHandler(someInput)));
newThread->start();
我遇到的问题是: …
我确实理解constexpr在运行时可以计算的表达式上使用它时的用法.
我想为复数创建一个constexpr.x = 5_i应该创建一个复杂数量的我自己创建的复杂类,并且我需要一个constantexpr constructor.
class Complex {
private:
double real_;
double imag_;
public:
...
Complex(double real, double imaginary);
constexpr Complex(double real, double imaginary):
real_(real),imag_(imaginary) {};
//Nonmember function
constexpr Complex operator""_i(long double arg);
在Complex(double real, double imaginary);稍后在.cpp文件中定义的.
当我尝试编译它时,我收到以下错误:
‘constexpr Complex::Complex(double, double)’ cannot be overloaded with
‘Complex::Complex(double, double)’
如果我只定义constexpr函数我的结论是我不能Complex::Complex(double, double)在运行时使用.
为什么我不能定义两个不同的功能？这在C++中是不允许的？编译器能否看到两个函数之间的区别？还有其他办法吗？
我在c ++中编写了一个不起作用的简单算法.我发现当我从我自己制作的自定义类中排序指向对象的列表时,它们会发生变化.或者更确切地说,列表更改为该类中的奇怪随机对象.
// ConsoleApplication45.cpp : Defines the entry point for the console application.
//
#include "stdafx.h"
#include <iostream>
#include <map>
#include <list>
#include <math.h>
using namespace std;
class LocationNode;
class NodeMap;
class LocationNode
{
private:
char name;
int xLocation;
int yLocation;
//map<LocationNode*,int> neighbors;
LocationNode* neighbors[100];
int neighborWeight[100];
int neighborCount;
LocationNode *previous;
int score;
int CalcDistance(LocationNode &dest)
{
return (int)sqrt(pow(dest.xLocation-xLocation,2) + pow(dest.yLocation-yLocation,2));
}
public:
int finalScore;
bool operator<(LocationNode const& rhs) const
{
// Use whatever makes sense for your application.
return …