[英]How to initialize a vector of struct inside another vector of struct?
I try to initialize structures of vectors that contains vector:我尝试初始化包含向量的向量结构:
struct productionCanvas
{
int canvasID;
int indexXmlJob;
};
struct productionArea
{
int areaID;
std::vector<productionCanvas> canvasList;
};
The first level is correctly initialized but not the second one:第一级已正确初始化,但第二级未正确初始化:
int areaIncr=0;
int canvasIncr=0;
std::vector<productionArea> production;
int addArea()
{
productionArea area{};
areaIncr++;
area.areaID = areaIncr;
area.canvasList = {};
production.push_back(area);
return areaIncr;
}
int addCanvas(int job)
{
productionCanvas canvas{};
canvasIncr++;
canvas.canvasID = canvasIncr;
canvas.indexXmlJob = job;
for (productionArea area : production)
{
if (area.areaID == areaIncr)
{
area.canvasList.push_back(canvas); // this line is triggered
break;
}
}
// Check if correctly push_back
for (productionArea area : production)
{
for (productionCanvas canvas : area.canvasList)
{
// This line is never triggered, why ?
}
}
return canvasIncr;
}
addArea(); // area correctly inserted
addCanvas(1); // canvas not inserted inside area
.
There is no return value of the push_back function, so I cannot know why it's not pushed back. push_back function没有返回值,所以我不知道为什么它没有被推回。 It seemed that it does not work like Qt-QVector.它似乎不像 Qt-QVector 那样工作。
How to initialize these struct?如何初始化这些结构?
You can zero-initialize any POD struct or array by simply adding {}
:您可以通过简单地添加{}
来对任何 POD 结构或数组进行零初始化:
productionArea area{};
// Or
productionArea area = {};
// Or
auto area = productionArea{};
Unless you are working in C/C++ environment, there is no need for typedef struct
in C++.除非您在 C/C++ 环境中工作,否则 C++ 中不需要typedef struct
。 The symbol namespaces are not separate.符号命名空间不是分开的。 This is equal to your current code:这等于您当前的代码:
struct productionCanvas_def
{
int canvasID;
int indexXmlJob;
} productionCanvas;
You can even initialize each member:你甚至可以初始化每个成员:
struct foo{
int a{2};
int a{4};
};
But then it is no longer POD.但后来它不再是 POD。
The problem is here:问题在这里:
for (productionArea area : production) // <-- The `area` is a copy of
// the one in the container.
{
if (area.areaID == areaIncr)
{
area.canvasList.push_back(canvas); // this line is triggered
break;
}
}
To modify elements in place, you have to use references for(productionArea &area: production)
要就地修改元素,您必须使用参考for(productionArea &area: production)
it doesn't look like c++, but the below code wiil not run as your canvasList with empty in addArea它看起来不像 c++,但下面的代码不会作为你的 canvasList 运行,addArea 中为空
area.canvasList = {};
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