CODEWITHSUNDEEP
c++buffercin
notamathwiz
notamathwiz

Reputation: 235

why is my compiler complaining when i try to clear the cin buffer

i am writing a program where i am trying to implement the following code:

int main(){

string inputcmd;


while (getline(cin, inputcmd)){
    cout << "TYPE A COMMAND" << endl;   
    cin >> inputcmd;

    cin.ignore (std::numeric_limits<std::streamsize>::max(), '\n'); 

    if (inputcmd == "make"){
        cout << "MAKING NEW PROJECT" << endl;
        get_project(cin);
    }

    else if (inputcmd == "retrieve"){
        cout << "RETRIEVING YOUR PROJECT" << endl;
    }
}

return 0;
}

i am trying to use the cin.ignore property to clear the buffer of the newline character currently residing in the buffer at that given time, however when i try and compile it is giving me a bunch of gibberish compiler error? why is this how can i fix this?

Upvotes: 0

Views: 100

Answers (3)

Constantin
Constantin

Reputation: 8961

You're using a strange combination of getline and cin... If you're using getline, you don't have to call cin.ignore at all. Don't mix both like you did or you will get confusing results.

This example propably runs like you want:

#include <string>
#include <iostream>

using namespace std;

int main(){
  string inputcmd;
  bool running = true;
  while (running){
    cout << "TYPE A COMMAND" << endl;
    getline(cin, inputcmd);
    if (inputcmd.substr(0, inputcmd.find(" ")) == "make"){
      if(inputcmd.find(" ")!=string::npos){
        inputcmd = inputcmd.substr(inputcmd.find(" ")+1);
        cout << "MAKING NEW PROJECT: " << inputcmd << endl;
        //get_project(cin);
      }else{
        cout << "make: not enough arguments" << endl;
      }
    }else if (inputcmd == "retrieve"){
      cout << "RETRIEVING YOUR PROJECT" << endl;
    }else if(inputcmd == ""){
      running = false;
    }
  }
  return 0;
}

Upvotes: 0

Some programmer dude
Some programmer dude

Reputation: 409166

You need to press an extra newline because you read the input twice. First with getline and a second time with cin >> ....

If you can have arguments to the commands, I recommend you remove the cin >> ... part, together with the cin.ignore() call, and use only getline and std::istringstream:

std::cout << "Enter command: ";
while (std::getline(std::cin, line))
{
    std::istringstream iss(line);

    // Get the command
    std::string command;
    iss >> command;

    if (command == "make")
    {
        ...
    }
    ...

    std::cout << "Enter command: ";
}

This way, you can easily get the space-separated arguments to the command as well.

And yes, you have code to print the prompt twice, but that is a smaller and negligible problem in my opinion.

Or if you want to be even more general, use e.g. a std::vector to store the command and arguments, and do something like

std::cout << "Enter command: ";
while (std::getline(cin, line))
{
    std::istringstream iss(line);

    std::vector<std::string> args;

    // Get the command and all arguments, and put them into the `args` vector
    std::copy(std::istream_iterator<std::string>(iss),
              std::istream_iterator<std::string>(),
              std::back_inserter(args));

    if (args[0] == "make")
    {
        ...
    }
    ...

    std::cout << "Enter command: ";
}

See e.g. these references:

Upvotes: 0

CroCo
CroCo

Reputation: 5741

Assuming you included 

#include <string>
#include <iostream>
using namespace std;

Then I'm not getting any error.

Upvotes: 1

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