Piping filename from standard input in linux into c++

Question

I want to be able to write a line in a terminal (as below) that takes a text file in the same directory and inputs its name into an executable file.

cat fileName | executable

I want to be able to read the fileName into c++ code. I already have a code that accesses the lines and reads through the file, it is just receiving fileName from the standard input.

Is there a line of code or a function to read the fileName into a c++ program and store it as a string? I am currently using the below code to read through each line of the text file.

ifstream myfile; 
myfile.open(fileName.c_str());

if( myfile.is_open() )
{   
    while ( getline (myfile ,line) )
    {
                  ......
    }
}

Answer 1

When you do cat filename | executable you are not sending the name of the file to your executable, but its contents. If you wish to send the name, use echo filename | executable or executable filename. Then you can process argc and argv as usual, and do the normal file reading you are showing in your example code.

Answer 2

All you need to do is read from stdin into a variable (e.g. "fname"):

int main () {
  string fname;
  cin >> fname
  ifstream myfile;
  myfile.open (fname);
  if (myfile.is_open() ) {   
    while ( getline (myfile, line) ) {
      ...

To accomodate either "pipe the name" or "use argc/argv" (as many *nix commands do):

int main (int argc, char *argv[]) {
  string fname;
  if (argc == 1) {
    cin >> fname
  }
  else {
    fname = argv[1];
  }
  ifstream myfile;
  myfile.open (fname);
  if (myfile.is_open() ) {   
    while ( getline (myfile, line) ) {
      ...

Answer 3

You're actually unclear, if you want to read the file from std::cin as it would be supplied by

cat filename | executable

or if you actually get the filename to be opened passed from std::cin.

Most likely you want to have an optional command line parameter (passed to int main(int argc, char* argv[])), and have your reading code rely to a std::istream input source, rather than std::cin or std::ifstream hardcoded.