I have read the answers for this question but I'm wondering if there is a better way to do this using standard c++ libs? Preferably without trying to open the file at all.
Edit: Thanks for the answers so far, but I'm still stuck... Both "stat" and "access" is pretty much ungoogleable. What should I #include to use these?
Use stat(), if it is cross-platform enough for your needs. It is not C++ standard though, but POSIX.
On MS Windows there is _stat, _stat64, _stati64, _wstat, _wstat64, _wstati64.
Use boost::filesystem:
if ( !boost::filesystem::exists( "myfile.txt" ) )
{
std::cout << "Can't find my file!" << std::endl;
}
How about access?
#include <io.h>
if (_access(filename, 0) == -1)
{
// File does not exist
}
To help with your problems googling, try adding "man page" to the search - if you're on Linux, the "man" command is your friend.
I would reconsider trying to find out if a file exists. Instead, you should try to open it (in Standard C or C++) in the same mode you intend to use it. What use is knowing that the file exists if, say, it isn't writable when you need to use it?
I am a happy boost user and would certainly use Andreas' solution. But if you didn't have access to the boost libs you can use the stream library:
ifstream file(argv[1]);
if (!file)
{
// Can't open file
}
It's not quite as nice as boost::filesystem::exists since the file will actually be opened...but then that's usually the next thing you want to do anyway.
Be careful of race conditions: if the file disappears between the "exists" check and the time you open it, your program will fail unexpectedly.
It's better to go and open the file, check for failure and if all is good then do something with the file. It's even more important with security-critical code.
Details about security and race conditions: http://www.ibm.com/developerworks/library/l-sprace.html