Using a C++ .exe with C++ : C++ception [duplicate] - c++

Question

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launch an exe/process with stdin stdout and stderr?
(3 answers)
Closed 8 years ago.
I need some help on this subject.
I have a C++ .exe that I want to open with C++ and then write some arguments in the console.
Here is an example of what I want to do:
Lets assume an executable whatsyourage.exe with this code (in reallity, I don't have the corresponding code):
#include <iostream>
using namespace std;
int main()
{
int age = 0;
cout << "What's your age ?" << endl;
cin >> age;
cout << "You are " << age << " year !" << endl;
return 0;
}
and I want to do something like:
int main()
{std::string invit="21";
std::string chemin ="whatsyourage.exe";// in the same library
std::string const command = chemin+" "+ invit;
system(command.c_str());
}
I want to write the age (21).
Can someone please help me?
Here is the answer:
int main()
{std::string invit="21";
std::string chemin ="whatsyourage.exe";
FILE* pipe = _popen(chemin.c_str(), "w");
if (pipe == NULL) {
perror("popen");
exit(1);
}
fputs("30", pipe);// write the age into the pipeline
pclose(pipe); // close the pipe
}

Answer 1

The popen() function from POSIX does what you are looking for. It allows you to execute a program (like system) while getting a file handle on its input/output streams.
For Windows, if popen() is not available, you can use the CreatePipe() & co functions to do the same thing; check out this question for some pointers.

Answer 2

The second snippet you added is good, and the problem is with the first code. In order to handle the command line from a program, you have to define the main as int main(int numberOfArguments, char* arguments[]) (often people use the shorter version - main(int argc, char* argv[]), but you can name the arguments as you wish). Then, if you pass an argument to the function, it will be in argv[1], since argv[0] is always the path to the executable. So the first program should look like this:
int main(int numberOfArguments, char* arguments[])
{
if(numberOfArguments>=2)
cout << "You are " << arguments[1] << " year !" << endl;
else
cout << "Too few arguments passed!" << endl;
return 0;
}