I am writing a C++ application and I need to read the result of a system command.
I am using popen()
more or less as shown here:
const int MAX_BUFFER = 2048;
string cmd="ls -l";
char buffer[MAX_BUFFER];
FILE *stream = popen(cmd.c_str(), "r");
if (stream){
while (!feof(stream))
{
if (fgets(buffer, MAX_BUFFER, stream) != NULL)
{
//here is all my code
}
}
pclose(stream);
}
I've been trying to re-write this in a different way. I saw some non-standard solutions like:
FILE *myfile;
std::fstream fileStream(myfile);
std::string mystring;
while(std::getline(myfile,mystring))
{
// .... Here I do what I need
}
My compiler does not accept this though.
How can I read from popen
in C++?
Your example:
FILE *myfile;
std::fstream fileStream(myfile);
std::string mystring;
while(std::getline(myfile,mystring))
Does't work because although you're very close the standard library doesn't provide an fstream
that can be constructed from a FILE*
. Boost iostreams does however provide an iostream
that can be constructed from a file descriptor and you can get one from a FILE*
by calling fileno
.
E.g.:
typedef boost::iostreams::stream<boost::iostreams::file_descriptor_sink>
boost_stream;
FILE *myfile;
// make sure to popen and it succeeds
boost_stream stream(fileno(myfile));
stream.set_auto_close(false); // https://svn.boost.org/trac/boost/ticket/3517
std::string mystring;
while(std::getline(stream,mystring))
Don't forget to pclose
later still.
Note: Newer versions of boost have deprecated the constructor which takes just a fd
. Instead you need to pass one of boost::iostreams::never_close_handle
or boost::iostreams::close_handle
as a mandatory second argument to the constructor.