C++调用外部exe

#include
#include
using namespace std;
int main(){
    double st=clock();
    for (int i=0;i<1;++i){
        char *str = "D:/Program Files (x86)/Tencent/QQ/Bin/QQ.exe";
        ShellExecute(NULL,NULL,str,NULL,NULL,SW_SHOW);
    }
    double ed=clock();
    cout<<(ed-st)/CLOCKS_PER_SEC<