C++ lambda函數，效率也許不如想象的好

C++ lambda函數，當函數參數用複製的方式捕獲時，參數存放在哪裡呢？

開始以為在棧裡，好像不對。

帶著這個疑問，寫一段遞迴函式，將參數的地址打出來看看。

參考代碼如下：

#include <stdio.h> #include <functional> void fun2( std::function<void()> callback ) {     (callback)(); } void fun1(int n) {     if(n <= 0) return;     printf("stack address = %p, ", &n);     fun2([n]() {         printf("capture address = %p\n", &n);         fun1(n - 1);     }); } int main() {     fun1(200);     return 0; }

(編譯環境：mingw64， 版本x64-4.8.0-release-posix-seh-rev2）

結果令人吃驚。以下為輸出結果，注意捕獲參數的地址，並不在程式的stack地區，

並且地址還不總是連續的。

很明顯，lambda表達的複製捕獲的參數，是動態分配出空間存放的。

特別關注效率或動態分配的場合，還是小心為妙。現實很骨感。

stack address = 000000000022F1E0, capture address = 00000000002F6D20stack address = 000000000022F0C0, capture address = 00000000002F6D40stack address = 000000000022EFA0, capture address = 00000000002F6D60stack address = 000000000022EE80, capture address = 00000000002F6D80stack address = 000000000022ED60, capture address = 00000000002F6DA0stack address = 000000000022EC40, capture address = 00000000002F6DC0stack address = 000000000022EB20, capture address = 00000000007A7810stack address = 000000000022EA00, capture address = 00000000007A7820stack address = 000000000022E8E0, capture address = 00000000007A7830stack address = 000000000022E7C0, capture address = 00000000007A7840

(轉載請標明：http://www.cnblogs.com/xhawk18/)