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V812. Decreased performance. Ineffective use of the 'count' function. It can possibly be replaced by the call to the 'find' function.
The analyzer has detected a construct that can be optimized: a call of the 'count' or 'count_if' function from the standard library is compared to zero. A slowdown may occur here, as these functions need to process the whole container to count the number of the necessary items. If the value returned by the function is compared to zero, we are interested to know if there is at least 1 item we look for or if there are no such items at all. This operation may be done in a more efficient way by using calls of the 'find' or 'find_if' functions.
Here's an example of non-optimal code:
void foo(const std::multiset<int> &ms)
{
if (ms.count(10) != 0)
{
....
}
}To make it faster we need to replace the non-optimal expression with a similar one using a more appropriate function - 'find' in this case. This is the optimized code:
void foo(const std::multiset<int> &ms)
{
if (ms.find(10) != ms.end())
{
....
}
}The following code sample is also non-optimal:
void foo(const std::vector<int> &v)
{
if (count(v.begin(), v.end(), 10) != 0)
{
....
}
}Optimization can be done in the same way as in the previous example. This is what the optimized code will look like:
void foo(const std::vector<int> &v)
{
if (find(v.begin(), v.end(), 10) != v.end())
{
....
}
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