How can I get a file's size in C++? [duplicate

问题:

This question already has an answer here:

• tellg() function give wrong size of file? 4 answers

Let's create a complementary question to this one. What is the most common way to get the file size in C++? Before answering, make sure it is portable (may be executed on Unix, Mac and Windows), reliable, easy to understand and without library dependencies (no boost or qt, but for instance glib is ok since it is portable library).

回答1:

#include <fstream>

std::ifstream::pos_type filesize(const char* filename)
{
    std::ifstream in(filename, std::ifstream::ate | std::ifstream::binary);
    return in.tellg(); 
}

See http://www.cplusplus.com/doc/tutorial/files/ for more information on files in C++.

回答2:

While not necessarily the most popular method, I've heard that the ftell, fseek method may not always give accurate results in some circumstances. Specifically, if an already opened file is used and the size needs to be worked out on that and it happens to be opened as a text file, then it's going to give out wrong answers.

The following methods should always work as stat is part of the c runtime library on Windows, Mac and Linux.

long GetFileSize(std::string filename)
{
    struct stat stat_buf;
    int rc = stat(filename.c_str(), &stat_buf);
    return rc == 0 ? stat_buf.st_size : -1;
}

or 

long FdGetFileSize(int fd)
{
    struct stat stat_buf;
    int rc = fstat(fd, &stat_buf);
    return rc == 0 ? stat_buf.st_size : -1;
}

On some systems there is also a stat64/fstat64. So if you need this for very large files you may want to look at using those.

回答3:

It is also possible to find that out using the fopen(),fseek() and ftell() function.

int get_file_size(std::string filename) // path to file
{
    FILE *p_file = NULL;
    p_file = fopen(filename.c_str(),"rb");
    fseek(p_file,0,SEEK_END);
    int size = ftell(p_file);
    fclose(p_file);
    return size;
}

回答4:

Using the C++ filesystem TS:

#include <experimental/filesystem>
namespace fs = std::experimental::filesystem;

int main(int argc, char *argv[]) {
  fs::path p{argv[1]};
  p = fs::canonical(p);

  std::cout << "The size of " << p.u8string() << " is " <<
      fs::file_size(p) << " bytes.\n";
}

回答5:

#include <stdio.h>
int main()
{
    FILE *f;
    f = fopen("mainfinal.c" , "r");
    fseek(f, 0, SEEK_END);
    unsigned long len = (unsigned long)ftell(f);
    printf("%ld\n", len);
    fclose(f);
}

回答6:

In c++ you can use following function, it will return the size of you file in bytes.

#include <fstream>

int fileSize(const char *add){
    ifstream mySource;
    mySource.open(add, ios_base::binary);
    mySource.seekg(0,ios_base::end);
    int size = mySource.tellg();
    mySource.close();
    return size;
}

回答7:

The code snippet below exactly addresses the question in this post :)

///
/// Get me my file size in bytes (long long to support any file size supported by your OS.
///
long long Logger::getFileSize()
{
    std::streampos fsize = 0;

    std::ifstream myfile ("myfile.txt", ios::in);  // File is of type const char*

    fsize = myfile.tellg();         // The file pointer is currently at the beginning
    myfile.seekg(0, ios::end);      // Place the file pointer at the end of file

    fsize = myfile.tellg() - fsize;
    myfile.close();

    static_assert(sizeof(fsize) >= sizeof(long long), "Oops.");

    cout << "size is: " << fsize << " bytes.\n";
    return fsize;
}