File size computation benchmark: C two times slower than C++? -


consider following code 3 different versions of file size computation. 

#include <iostream> #include <cstdio> #include <string> #include <fstream>  inline long long int filesize1(const std::string& filename) {     std::ifstream filestream(filename.c_str(), std::ios::binary);     std::streampos first = 0;     std::streampos last = 0;     long long int size = -1;     if (filestream.is_open()) {         filestream.seekg(0, std::ios::beg);         first = filestream.tellg();         filestream.seekg(0, std::ios::end);         last = filestream.tellg();         if ((first != -1) && (last != -1) && (last-first >= 0)) {             size = last-first;         }         filestream.close();     }     return size; }  inline long long int filesize2(const std::string& filename) {     std::ifstream filestream(filename.c_str(), std::ios::binary);     return (filestream) ? (static_cast<long long int>(filestream.seekg(0, std::ios::end).tellg()-filestream.seekg(0, std::ios::beg).tellg())) : (-1ll); }  inline long long int filesize3(const std::string& filename) {     std::file* file = std::fopen(filename.c_str(), "rb");     long long int size = -1;     if (file) {         std::fseek(file, 0, seek_end);         size = std::ftell(file);         std::fclose(file);     }     return size; }  int main(int argc, char* argv[]) {     unsigned int n = 0;     switch (std::atoi(argv[1])) {         case 1: (int = 0; < std::atoi(argv[3]); ++i) n += filesize1(argv[2]); break;         case 2: (int = 0; < std::atoi(argv[3]); ++i) n += filesize2(argv[2]); break;         case 3: (int = 0; < std::atoi(argv[3]); ++i) n += filesize3(argv[2]); break;     }     std::cout<<n<<std::endl;     return 0; }

first question : have guarantee in cases have same result 3 different versions ?

second question : why version 3 in c approximately 2 times slower first 2 versions ?


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