I want to take argv[(2 in this example)], store it into vector and use it later in program. The problem is that no operand matches those operands std::string == int. So does that mean that the app sees '-r' as int? I'm a bit confused here.
int main(int argc, char* argv[])
{
std::vector<std::string> argList;
cout<<"argc: "<<argc<<endl;
for(int i=2; i<=argc; i++)
{
argList.push_back(argv[i]);
}
if(argList.at(2) == '-r') cout<<" Good job ";
}
There are several issues with your program:
i until i == argc, that will attempt to construct a string from argv[argc], a NULL pointer due to the requirement by C and C++ standards that argv[argc] be 0 (NULL), see this SO question. argv is an array with argc pointers to null-terminated character strings (terminated by ASCII NUL, 0), the array itself is terminated with a NULL pointer (not counted in argc). Now, in C++ you can construct a string from a pointer to a null-terminated character string, but passing a NULL pointer to a string constructor results in undefined behavior, see this SO question, also see the list of std::string constructors here, you are implicitly using constructor (4) in that list (from c-string).i==2, which means argList[0] will contain argv[2], you then reference argList.at(2), which would correspond to argv[4], this is not likely what you meant.I've corrected these and created a working program, click here
#include <iostream>
#include <vector>
#include <string>
using std::vector;
using std::string;
using std::cout;
using std::endl;
int main(int argc, char* argv[])
{
vector<string> argList;
cout << "argc: " << argc << endl;
for(int i=0; i < argc; ++i)
{
argList.push_back(argv[i]);
}
cout << "Program name is " << argList[0] << endl;
if(argc > 1) {
if(argList.at(1) == "-r") {
cout << " Good job, you supplied -r\n";
} else {
cout << "Unrecognized option " << argList[1]
<< "\nUsage: " << argList[0] << " -r\n";
}
}
return 0;
}
argv[argc] invokes undefined behavior and you cannot make assumptions as to what that next bit of memory contains.
5.1.2.2.1 Program startup of C Standard (draft) open-std.org/jtc1/sc22/wg14/www/docs/n1124.pdf says "argv[argc] shall be a null pointer."The problem is your use of single quotes in '-r'. You want double quotes here:
if(argList.at(2) == "-r") cout<<" Good job ";
The reason is that in C++, single quotes are used for characters only. There is such a thing as a "multi-byte character constant", which is what '-r' ends up being. This is something completely different from a string constant, which is what you want.
"-r". With single quotes, it's a literal of type int.charthat can be autoboxed into an int.intisn't an object anyway.