Parsing command line arguments in C++

Question

Below is the sample code that I tried to solve. Calculation of grades of students using stl maps.

#include <iostream>
#include <iterator>
#include <map>
#include <vector>
#include <set>
#include <algorithm>
#include <cmath>
#include <string>

using namespace std;

int main()

{

typedef map<string, int>mapType;
mapType calculator;

int level;
string name;

//Student and Marks:
calculator.insert(make_pair("Rita", 142));
calculator.insert(make_pair("Anna", 154));
calculator.insert(make_pair("Joseph", 73));
calculator.insert(make_pair("Markus", 50));
calculator.insert(make_pair("Mathias", 171));
calculator.insert(make_pair("Ruben", 192));
calculator.insert(make_pair("Lisa", 110));
calculator.insert(make_pair("Carla", 58));

mapType::iterator iter = --calculator.end();
calculator.erase(iter);


for (iter = calculator.begin(); iter != calculator.end(); ++iter) {
    cout << iter->first << ": " << iter->second << "g\n";
}
cout << "Choose a student name :" << '\n';
getline(cin, name);

iter = calculator.find(name);
if (iter == calculator.end())
    cout << "The entered name is not in the list" << '\n';
else
    cout << "Enter the level :";
cin >> level;

cout << "The final grade is " << iter->marks * level << ".\n";

}

Now I want to assume that my program takes in 2 arguments like student name and level. Something like

$./calculator --student-name Rita --level 3

And my output should be something like marks*level. I tried doing a small piece of code separately but I am not getting it right.

using namespace std;

const char* studentName ="--student-name";
int main(int argc,char* argv[])
{
int counter;
if(argc==1)
    printf("\nNo Extra Command Line Argument Passed Other Than Program Name");
if(argc>=2)
{

        printf("%s\n",argv[1]);
                if(std::argv[1] == "--student-name")
                {
                    printf("print nothing");
                }
                else if(argv[1]=="--level")
                {
                    printf("%s",argv[2]);
                }

}
return 0;
}

Anyone can guide me on this. Thanks!

To compare two C strings you should use the function strcmp. — Vlad from Moscow
– Vlad from Moscow, Commented Jun 14, 2020 at 18:06

Vlad from Moscow · Accepted Answer · 2020-06-14 18:52:01Z

1

For example in this if statement

if(std::argv[1] == "--student-name")

(where you are using incorrectly the qualified name std::argv[1] of the local (block scope) variable argv instead of just argv[1]) there are compared two addresses: the first one is of the string pointed to by argv[1] and the second one is the address of the first character of the string literal "--student-name". As these are two different objects then their addresses are different,

To compare C strings you need to use the standard C function strcmp declared in the header <cstring>.

For example

#include <cstring>

//...

if( std::strcmp( argv[1], "--student-name" ) == 0 )
// ...

edited Jun 14, 2020 at 18:52

answered Jun 14, 2020 at 18:11

Vlad from Moscow

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