passing const qstring as this
时间: 2023-04-29 14:06:44 浏览: 100
"passing const qstring as this" 的意思是将 const qstring 作为 this 参数传递。此处的 this 指的是指针,通常用于指向当前对象,而 const qstring 则表示一个不可变的字符串对象。
相关问题
QByteArray data = reply->readAll(); strResult = QString::fromUtf8(data);报错/home/ccy/daimabeifen/vtmmonitor_rizhishangchuan/vtmmonitor/CDownload.cpp:210: error: passing 'const QString' as 'this' argument discards qualifiers [-fpermissive] strResult = QString::fromUtf8(data); ^
这个错误是因为你的`strResult`变量被声明为常量,所以不能在其上调用非常量成员函数。你可以将其声明为非常量来解决这个问题,或者使用`const_cast`来去除常量性。下面是两种解决方案的示例:
1. 将`strResult`声明为非常量:
```c++
QString strResult;
QByteArray data = reply->readAll();
strResult = QString::fromUtf8(data);
```
2. 使用`const_cast`去除常量性:
```c++
const QString strResult;
QByteArray data = reply->readAll();
QString& nonConstStrResult = const_cast<QString&>(strResult);
nonConstStrResult = QString::fromUtf8(data);
```
但是,第二种解决方案并不是推荐的做法,如果不是必须去除常量性,最好还是使用第一种方法。
passing const qlist
Passing a `const QList` means that the function you are calling will not modify the elements of the QList. This is useful when you want to ensure that the QList is not modified accidentally or intentionally by the function. It also allows you to pass a temporary QList object as an argument to the function.
To pass a const QList, you can declare the function argument as `const QList<T> &list`. Here, `T` is the type of the elements in the list. The `&` symbol indicates that you are passing the list by reference, so the function can access the original list without making a copy of it. The `const` keyword before the QList indicates that the function will not modify the list.
For example, consider the following function that takes a const QList of integers as an argument:
```
void myFunction(const QList<int> &list)
{
// do something with the list
}
```
You can call this function with a const QList object as follows:
```
QList<int> myList = {1, 2, 3};
myFunction(myList);
```
This will work because `myList` is implicitly converted to a const reference to QList.