Reading popen results in C++ - c++

Question

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++?

Answer 1

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.

Answer 2

Here is something which i wrote long back, may help you. It might have some errors.
#include <vector>
#include <string>
#include <stdio.h>
#include <iostream>
bool my_popen (const std::string& cmd,std::vector<std::string>& out ) {
bool ret_boolValue = true;
FILE* fp;
const int SIZEBUF = 1234;
char buf [SIZEBUF];
out = std::vector<std::string> ();
if ((fp = popen(cmd.c_str (), "r")) == NULL) {
return false;
}
std::string cur_string = "";
while (fgets(buf, sizeof (buf), fp)) {
cur_string += buf;
}
out.push_back (cur_string.substr (0, cur_string.size () - 1));
pclose(fp);
return true;
}
int main ( int argc, char **argv) {
std::vector<std::string> output;
my_popen("ls -l > /dev/null ", output);
for ( std::vector<std::string>::iterator itr = output.begin();
itr != output.end();
++itr) {
std::cout << *itr << std::endl;
}
}