Lambda functions are a kind of anonymous functions in C++. These are mainly used as callbacks in C++. Lambda function is like a normal function i.e.
You can pass arguments to it
It can return the result
But it doesn’t have any name. Its mainly used when we have to create very small functions to pass as a callback to an another API.
Syntax of Lambda Function:
[ capture clause ] (parameters) -> return-type
{
definition of method
}
capture clause:
A lambda with empty capture clause [ ] can access only those variable which are local to it.
We can capture external variables from enclosing scope by three ways : Capture by reference Capture by value Capture by both (mixed capture)
Syntax used for capturing variables : [&] : capture all external variable by reference [=] : capture all external variable by value [a, &b] : capture a by value and b by reference
Parameters: we can pass the parameters in lambda function.
return-type:
return-type in lambda expression are evaluated by compiler itself and we don’t need to specify that explicitly and -> return-type part can be ignored but in some complex case as in conditional statement, compiler can’t make out the return type and we need to specify that.
Example:
#include <iostream>
#include <vector>
#include<algorithm>
using namespace std;
int main()
{
vector<int> v1 = {2,6,2,9,8,5};
for_each (v1.begin(),v1.end(),[](int x) {
x=x*2;
cout<<x<<endl;
});
}Generic Lambda(C++14):
#include <iostream>
using namespace std;
int main()
{
auto add = [](auto x,auto y)
{
return x+y;
};
cout<<add(10,20)<<endl;
cout<<add(10.5,20.8)<<endl;
return 0;
}
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