#include <map>
struct X {
int x;
bool operator < (const X v) const
{
return (x < v.x);
}
};
struct Y {
int y;
};
int main()
{
X x = {1};
Y y = {2};
std::map <X, Y> Z;
std::pair<std::map<X, Y>::iterator,bool> lastval;
// Insert a value
lastval = Z.insert(std::pair<X, Y>(x, y));
// Erase the "last" inserted item
Z.erase(lastval.first->first);
// Error: Check if last item was erased or if iterator is valid
if (lastval.first != Z.end())
{
/* ... */
}
}
我在检查最后插入的项目是否已删除时收到错误。有什么办法可以检查吗?
最佳答案
使用 map::erase
的返回值
if(Z.erase(lastval.first->first))
{
/* item has been erased */
}
或
// Erase the "last" inserted item
Z.erase(lastval.first->first);
if(Z.find(x) == Z.end())
{
/* item has been erased */
}
您还应该更改您的 operator<
至
bool operator < (const X& v) const
// ^
// take arg by reference to avoid unnecessary copying
关于c++ - 通过map key检查最后插入的项目是否存在,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/21298362/