1. 

std::string name("***.**");
std::string extension("**");

name.compare(name.size() - extension.size(), extension.size(), extension) == 0;

2.

#include <string.h>

char tmpStr[100];
strcpy(tmpStr,"***.**");
char* pext = std::strrchr(tmpStr, '.');
std::string extply("ply");
std::string extpcd("pcd");
if(pext){
    *pext='\0';
     pext++;
}
std::string ext(pext);
//如果不支援檔案格式，退出程式
if (!((ext == extply)||(ext == extpcd))){
    std::cout << "檔案格式不支援!" << std::endl;
    std::cout << "支援檔案格式：*.pcd和*.ply！" << std::endl;
    return(-1);
}