2

I am trying to run a simple lambda example.

// lambda.cpp
#include <functional>
//#include <tr1/functional> 

int main()
{
   // Assign the same lambda expression to a function object.
   function<int (int, int)> f2 = [] (int x, int y) { return x + y; };
   //function<int (int, int)> f2 = [] (int x, int y) { return x + y; };
}

I'm compiling it like this:

$ g++ -std=c++0x -fpermissive lamdas.cpp
lambdas.cpp: In function ‘int main()’:    
lambdas.cpp:10: error: expected primary-expression before ‘=’ token
lambdas.cpp:10: error: expected primary-expression before ‘[’ token
lambdas.cpp:10: error: expected primary-expression before ‘]’ token
lambdas.cpp:10: error: expected primary-expression before ‘int’
lambdas.cpp:10: error: expected primary-expression before ‘int’
lambdas.cpp:10: error: expected ‘;’ before ‘{’ token

How do I get it to compile with no errors?

Improve this question
8
  • 7
    What version of GNU c++ is this? I've never seen it spelling-correct source file names on the fly! Commented Jul 5, 2011 at 21:12
  • The lambda isn't the problem. You could replace it with something else, and you'd still get these errors. Commented Jul 5, 2011 at 21:12
  • @Tomalak: I think it's got style Commented Jul 5, 2011 at 21:13
  • 1
    @sehe: Hehe; they brought it in with C++0x support, guesstimating that the average human's ability to write basic words will completely vapourise after an hour with the new standard. Commented Jul 5, 2011 at 21:13
  • 1
    To be honest, I'm surprised the compiler did not substitute the equivalent ISO token Λάμβδα (or λ) in order to be totally standards conforming :) Commented Jul 5, 2011 at 21:47

3 Answers 3

Reset to default
5

Did you mean std::function?

Standard library features live in the std namespace.

It's also interesting that your copy/paste is clearly fake; you wrote "lamdas.cpp" then compiled "lambdas.cpp"!

Improve this answer
Sign up to request clarification or add additional context in comments.

5 Comments

He also has lambda.cpp at the top of his source file!!
@Marlon: Certainly a sign of indecision!
Also known by some as the "stood" namespace :(
@sehe: I am using GNU 4.4 version of c++.
@Sachin: Live example of the code working perfectly with std::.
2 
std::function<int (int, int)> f2 = [] (int x, int y) { return x + y; };

or, probably better

auto f2 = [] (int x, int y) { return x + y; };
Improve this answer

5 Comments

Dammit; it's past the 5 minute window in which I could have quietly stolen that good idea.
Worth remembering that the two alternatives are quite different.
Lambdas that don't capture anything are also implicitly convertible to function pointers.
@Tomalak: i tried using std::function but it doesn't seem to generate the same compile error. Agree on the file name error and the copy paste mistake as well.
@Sachin: Of course it doesn't generate the same compile error. std:: is the solution for the one you posted.
0

It looks to me like you forgot -std=c++0x.

Improve this answer

Comments

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Start asking to get answers

Find the answer to your question by asking.

Ask question

Explore related questions

See similar questions with these tags.