MSVC8中的SafeCode對性能的影響
    由于前面一篇關(guān)于編譯boost1.34.0編譯的blog
（http://www.shnenglu.com/chemz/archive/2007/06/06/25666.html ）
中有人提到在Visual C++ 2005中由于微軟采用了safe code技術(shù)會對性能產(chǎn)生非常大的影
響（下降50%），所以本著性能不可以通過估計(jì)和猜測來確定，所以編寫了一個(gè)針對于此的
測試程序進(jìn)行了測試。
    該測試程序?yàn)榱俗龅阶銐虻母采wC++標(biāo)準(zhǔn)庫中STL部分，所以選擇了容器/跌代器/算法三
個(gè)關(guān)鍵組成中的具有代表性的類和對象進(jìn)行了測試。首先解釋一下微軟所提供的safe code
的目的和作用，由于STL庫中為了考慮到性能的最大化所以對于像：邊界值檢查、合法性檢
查以及范圍檢查等都省略了，此部分需要依靠程序員自行處理，而safe code就是在STL設(shè)計(jì)
到此部分的代碼中添加了判斷用的語句（通過宏引入的）。究竟會不會影響到性能呢？有多
大的影響呢？
    測試代碼如下：
        #include <iostream>
        #include <ctime>
        #include <vector>
        #include <list>
        #include <map>
        #include <algorithm>
        
        #include <boost/lambda/lambda.hpp>
        #include <boost/lambda/bind.hpp>
       
        #define MAX_TEST_COUNT 1000 * 1000 * 2
        #define TIME_ELAPSE() ( std::clock() - start * 1.0 ) / CLOCKS_PER_SEC
       
        int main( int argc, char *argv[] )
        {
            double times[6];
            size_t idx = 0;
            /*
             * vector
             */
            std::vector<size_t> vec1;
            std::clock_t start = std::clock();
            {
                for ( size_t i = 0; i < MAX_TEST_COUNT; ++i )
                {
                    vec1.push_back( i );
                }
            }
            times[idx++] = TIME_ELAPSE();
       
            std::vector<std::string> vec2;
            start = std::clock();
            {
                for ( size_t i = 0; i < MAX_TEST_COUNT; ++i )
                {
                    vec2.push_back( "std::vector<std::string>" );
                }
            }
            times[idx++] = TIME_ELAPSE();
            /*
             * list
             */
            std::list<size_t> lst1;
            start = std::clock();
            {
                for ( size_t i = 0; i < MAX_TEST_COUNT; ++i )
                {
                    lst1.push_back( i );
                }
            }
            times[idx++] = TIME_ELAPSE();
       
            std::list<std::string> lst2;
            start = std::clock();
            {
                for ( size_t i = 0; i < MAX_TEST_COUNT; ++i )
                {
                    lst2.push_back( "std::vector<std::string>" );
                }
            }
            times[idx++] = TIME_ELAPSE();
            /*
             * map
             */
            std::map<size_t, size_t> map1;
            start = std::clock();
            {
                for ( size_t i = 0; i < MAX_TEST_COUNT; ++i )
                {
                    map1.insert( std::make_pair( i, i ) );
                }
            }
            times[idx++] = TIME_ELAPSE();
       
            std::map<size_t, std::string> map2;
            start = std::clock();
            {
                for ( size_t i = 0; i < MAX_TEST_COUNT; ++i )
                {
                    map2.insert( std::make_pair( i, "std::vector<std::string>" ) );
                }
            }
            times[idx++] = TIME_ELAPSE();
       
            std::cout << "std::vector<size_t>::push_back        " << times[0] << " s" << std::endl;
            std::cout << "std::vector<std::string>::push_back   " << times[1] << " s" << std::endl;
            std::cout << "std::list<size_t>::push_back          " << times[2] << " s" << std::endl;
            std::cout << "std::list<std::string>::push_back     " << times[3] << " s" << std::endl;
            std::cout << "std::map<size_t, size_t>::insert      " << times[4] << " s" << std::endl;
            std::cout << "std::map<size_t, std::string>::insert " << times[5] << " s" << std::endl;
       
            std::cout << std::endl;
            /*
             * iterator
             */
            idx = 0;
            start = std::clock();
            {
                for ( std::vector<size_t>::iterator it = vec1.begin(); it != vec1.end(); ++it )
                {
                    (*it) = (*it) + 1;
                }
            }
            times[idx++] = TIME_ELAPSE();
            start = std::clock();
            {
                for ( std::vector<std::string>::iterator it = vec2.begin(); it != vec2.end(); ++it )
                {
                    (*it) = "std::vector<std::string>::iterator";
                }
            }
            times[idx++] = TIME_ELAPSE();
            start = std::clock();
            {
                for ( std::list<size_t>::iterator it = lst1.begin(); it != lst1.end(); ++it )
                {
                    (*it) = (*it) + 1;
                }
            }
            times[idx++] = TIME_ELAPSE();
            start = std::clock();
            {
                for ( std::list<std::string>::iterator it = lst2.begin(); it != lst2.end(); ++it )
                {
                    (*it) = "std::list<std::string>::iterator";
                }
            }
            times[idx++] = TIME_ELAPSE();
            start = std::clock();
            {
                for ( std::map<size_t, size_t>::iterator it = map1.begin(); it != map1.end(); ++it )
                {
                    (*it).second = (*it).second + 1;
                }
            }
            times[idx++] = TIME_ELAPSE();
            start = std::clock();
            {
                for ( std::map<size_t, std::string>::iterator it = map2.begin(); it != map2.end(); ++it )
                {
                    (*it).second = "std::map<size_t, std::string>::iterator";
                }
            }
            times[idx++] = TIME_ELAPSE();
       
            std::cout << "std::vector<size_t>::iterator           " << times[0] << " s" << std::endl;
            std::cout << "std::vector<std::string>::iterator      " << times[1] << " s" << std::endl;
            std::cout << "std::list<size_t>::iterator             " << times[2] << " s" << std::endl;
            std::cout << "std::list<std::string>::iterator        " << times[3] << " s" << std::endl;
            std::cout << "std::map<size_t, size_t>::iterator      " << times[4] << " s" << std::endl;
            std::cout << "std::map<size_t, std::string>::iterator " << times[5] << " s" << std::endl;
       
            std::cout << std::endl;
            /*
             * for_each
             */
            using namespace boost::lambda;
            idx = 0;
       
            start = std::clock();
            {
                std::for_each( vec1.begin(), vec1.end(), _1 = _1 + 1 );
            }
            times[idx++] = TIME_ELAPSE();
            start = std::clock();
            {
                std::for_each( vec2.begin(), vec2.end(), _1 = "std::for_each" );
            }
            times[idx++] = TIME_ELAPSE();
            start = std::clock();
            {
                std::for_each( lst1.begin(), lst1.end(), _1 = _1 + 1 );
            }
            times[idx++] = TIME_ELAPSE();
            start = std::clock();
            {
                std::for_each( lst2.begin(), lst2.end(), _1 = "std::for_each" );
            }
            times[idx++] = TIME_ELAPSE();
            start = std::clock();
            {
                std::for_each( map1.begin(), map1.end(), bind( &std::map<size_t, size_t>::value_type::second, _1 ) = bind( &std::map<size_t, size_t>::value_type::second, _1 ) + 1 );
            }
            times[idx++] = TIME_ELAPSE();
            start = std::clock();
            {
                std::for_each( map2.begin(), map2.end(), bind( &std::map<size_t, std::string>::value_type::second, _1 ) = "std::for_each" );
            }
            times[idx++] = TIME_ELAPSE();
       
            std::cout << "std::vector<size_t>::for_each           " << times[0] << " s" << std::endl;
            std::cout << "std::vector<std::string>::for_each      " << times[1] << " s" << std::endl;
            std::cout << "std::list<size_t>::for_each             " << times[2] << " s" << std::endl;
            std::cout << "std::list<std::string>::for_each        " << times[3] << " s" << std::endl;
            std::cout << "std::map<size_t, size_t>::for_each      " << times[4] << " s" << std::endl;
            std::cout << "std::map<size_t, std::string>::for_each " << times[5] << " s" << std::endl;
       
            return 0;
        }
    我的測試環(huán)境如下：
        軟件環(huán)境：Visual Studio2005 Pro + SP1, boost1.34.0
        硬件環(huán)境：PentiumD 3.0GHz, 4G RAM
    測試數(shù)據(jù)：
        1. 默認(rèn)開啟safe code
           std::vector<size_t>::push_back        0.031 s
           std::vector<std::string>::push_back   2.609 s
           std::list<size_t>::push_back          0.797 s
           std::list<std::string>::push_back     2.813 s
           std::map<size_t, size_t>::insert      1.906 s
           std::map<size_t, std::string>::insert 4.047 s

           std::vector<size_t>::iterator           0 s
           std::vector<std::string>::iterator      1.718 s
           std::list<size_t>::iterator             0.016 s
           std::list<std::string>::iterator        1.734 s
           std::map<size_t, size_t>::iterator      0.063 s
           std::map<size_t, std::string>::iterator 1.891 s

           std::vector<size_t>::for_each           0.015 s
           std::vector<std::string>::for_each      0.156 s
           std::list<size_t>::for_each             0.016 s
           std::list<std::string>::for_each        0.156 s
           std::map<size_t, size_t>::for_each      0.078 s
           std::map<size_t, std::string>::for_each 0.313 s

        2. 關(guān)閉safe code（通過定義如下宏：_CRT_SECURE_NO_DEPRECATE,
                                          _SCL_SECURE_NO_DEPRECATE,
                                          _SECURE_SCL=0）
           std::vector<size_t>::push_back        0.031 s
           std::vector<std::string>::push_back   2.594 s
           std::list<size_t>::push_back          0.796 s
           std::list<std::string>::push_back     2.813 s
           std::map<size_t, size_t>::insert      1.875 s
           std::map<size_t, std::string>::insert 4.047 s

           std::vector<size_t>::iterator           0 s
           std::vector<std::string>::iterator      1.703 s
           std::list<size_t>::iterator             0.031 s
           std::list<std::string>::iterator        1.719 s
           std::map<size_t, size_t>::iterator      0.062 s
           std::map<size_t, std::string>::iterator 1.891 s

           std::vector<size_t>::for_each           0.016 s
           std::vector<std::string>::for_each      0.14 s
           std::list<size_t>::for_each             0.016 s
           std::list<std::string>::for_each        0.172 s
           std::map<size_t, size_t>::for_each      0.062 s
           std::map<size_t, std::string>::for_each 0.313 s

    由上面的測試數(shù)據(jù)可以的出如下的結(jié)論：
    1. safe code對代碼的性能確實(shí)是有影響的，畢竟加入了判斷的代碼；
    2. safe code對代碼的性能影響非常的小（最大沒有超過5%），基本上為了安全型可以
       忽略其影響，如果確實(shí)比較注重性能，可以考慮在release版本下關(guān)閉safe code檢查，
       在debug版下還是打開以發(fā)現(xiàn)錯(cuò)誤比較好。
 
注：宏解釋
    _CRT_SECURE_NO_DEPRECATE和_SCL_SECURE_NO_DEPRECATE用于關(guān)閉safe code代碼警告；
    _SECURE_SCL用于控制是否采用safe code對STL邊界進(jìn)行檢查。