Portable way to get file size in C/C++
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19-09-2019 - |
Question
I need to determin the byte size of a file.
The coding language is C++ and the code should work with Linux, windows and any other operating system. This implies using standard C or C++ functions/classes.
This trivial need has apparently no trivial solution.
Solution
Using std's stream you can use:
std::ifstream ifile(....);
ifile.seekg(0, std::ios_base::end);//seek to end
//now get current position as length of file
ifile.tellg();
If you deal with write only file (std::ofstream), then methods are some another:
ofile.seekp(0, std::ios_base::end);
ofile.tellp();
OTHER TIPS
You can use stat system call:
#ifdef WIN32
_stat64()
#else
stat64()
If you only need the file size this is certainly overkill but in general I would go with Boost.Filesystem for platform-independent file operations. Amongst other attribute functions it contains
template <class Path> uintmax_t file_size(const Path& p);
You can find the reference here. Although Boost Libraries may seem huge I found it to often implement things very efficiently. You could also only extract the function you need but this might proof difficult as Boost is rather complex.
Simples:
std::ifstream ifs;
ifs.open("mybigfile.txt", std::ios::bin);
ifs.seekg(0, std::ios::end);
std::fpos pos = ifs.tellg();
Often we want to get things done in the most portable manner, but in certain situations, especially like this, I would strongly recommend using system API's for best performance.
Portability requires you to use the least common denominators, which would be C. (not c++) The method that I use is the following.
#include <stdio.h>
long filesize(const char *filename)
{
FILE *f = fopen(filename,"rb"); /* open the file in read only */
long size = 0;
if (fseek(f,0,SEEK_END)==0) /* seek was successful */
size = ftell(f);
fclose(f);
return size;
}