Equals returning false in c++ - c++

Question

I'm fairly new to cpp and I am trying to do a project. It says that the code must take in a filename as an argument and will be run by:
./main -i filename
I have written a for-loop that will iterate through the list of arguments to find the "-i" argument so that I can determine the filename. But this line always return false:
argv[i] == "-i"
Below is my code:
#include <string>
#include <iostream>
int main(int argc, char *argv[]) {
std::string test = argv[0];
for(int i = 0; i < argc; i++){
if(argv[i] == "-i"){
test = argv[i+1];
break;
}
}
std::cout << test;
return 1;
}

Answer 1

argv[i] == "-i"
In the line above you compare two pointers: char* and const char*, respectively.
In other words, instead of comparing argv[i] and "-i" two pointers are compared which are pretty much unlikely to point to the same location. As a result, the check doesn't work in your case.
You can fix it in multiple ways, for example wrap "-i" into std::string to make the comparison work properly:
const auto arg = std::string{ "-i" };
for(int i = 0; i < argc; i++){
if(argv[i] == arg){
test = argv[i+1];
break;
}
}
Starting with C++17 you might also use a std::string_view:
const std::string_view sv{ "-i" };
for(int i = 0; i < argc; i++){
if(argv[i] == sv){
test = argv[i+1];
break;
}
}
which is a preferable way as it avoids a std::string creation.

Answer 2

You cannot compare pointers to char to string literals (char const*) using ==. Use std::strcmp() (<cstring>) or construct a std::string (<string>) from it to make it comparable to a char* using ==.

Answer 3

try this:
#include <iostream>
#include <string>
using namespace std;
int main(int argc, char *argv[]) {
string test;
for(int i = 0; i < argc; i++){
cout << "\n" << argv[i] << endl;
if((string)argv[i] == "-i"){
test = argv[i + 1];
cout << "test= " << test << endl;
break;
}
}
cout << test << endl;
system("pause");
return 0;
}