C ++ 11 lambdas到函数指针 [英] C++11 lambdas to Function Pointer

问题描述

我开始使用C ++ 11 lambdas开发应用程序，并需要将一些类型转换为函数指针。这在GCC 4.6.0中完美地工作：

I'm starting to develop applications using C++11 lambdas, and need to convert some types to function pointers. This works perfectly in GCC 4.6.0:

void (* test)() = []()
{
    puts("Test!");
};

test();

我的问题是当我需要在lambda中使用函数或方法局部变量：

My problem is when I need to use function or method local variables within the lambda:

const char * text = "test!";

void (* test)() = [&]()
{
    puts(text);
};

test();

G ++ 4.6.0会显示投放错误代码：

G++ 4.6.0 gives the cast error code:

main.cpp: In function 'void init(int)':
main.cpp:10:2: error: cannot convert 'main(int argc, char ** argv)::<lambda()>' to 'void (*)()' in initialization

$ b b

如果使用自动，它可以正常工作：

const char * text = "Test!";

auto test = [&]()
{
    puts(text);
};

test();

我的问题是：如何使用 [& ？在我的情况下，我不能使用STL std :: function （因为我的程序不使用C ++ RTTI和EXCEPTIONS运行时），它有一个简单的函数实现来解决这个问题？ p>

My question is: how can I create a type for a lambda with [&]? In my case, I can not use the STL std::function (because my program does not use C++ RTTI and EXCEPTIONS runtime), and It has a simple implementation of function to solve this problem?

推荐答案

我不能使用STL std :: function（因为我的程序不使用C ++ RTTI和EXCEPTIONS runtime）

I can not use the STL std::function (because my program does not use C++ RTTI and EXCEPTIONS runtime)

然后您可能需要编写自己的 std :: function 。

Then you may need to write your own equivalent to std::function.

对于 std :: function ，类型擦除的通常实现不需要RTTI的功能;它通过常规的虚函数调用工作。所以写自己的版本是可行的。

The usual implementation of type erasure for std::function doesn't need RTTI for most of its functionality; it works through regular virtual function calls. So writing your own version is doable.

的确， std :: function 需要 RTTI是 target_type 和 target 函数，这不是世界上最有用的函数。您可以使用 std :: function 而不调用这些函数，假设您使用的实现不需要RTTI的常规业务。

Indeed, the only things in std::function that need RTTI are the target_type and target functions, which are not the most useful functions in the world. You might be able to just use std::function without calling these functions, assuming that the implementation you're using doesn't need RTTI for its usual business.

通常，当您禁用异常处理时，程序会在遇到 throw 语句时关闭并抛出错误。因为大多数 std :: function 会发出的异常不是你能够恢复的那种异常（调用一个空的 function ，内存不足等），你可以使用 std :: function 。

Typically, when you disable exception handling, the program simply shuts down and errors out when encountering a throw statement. And since most of the exceptions that a std::function would emit aren't the kind of thing you would be able to recover from (calling an empty function, running out of memory, etc), you can probably just use std::function as is.

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