C++: Convert multiple command line arguments from a single std::stringstream

Question

I have a program which inputs multiple string and numeric variables from the command line. As I want to convert few inputs to numeric types, I have been using std::stringstream as suggested at learncpp . Presently, my code looks something like:

main.cpp

int main(int argc, char* argv[]) {
if (argc != 7)
{
     std::cout << "Execute the program in the following format:\n";
     std::cout << ".\segment inputImage outputDir color k sigma minSize\n";
     std::cout << "Exiting program\n";
     std::exit(1);
}

float gaussianBlur, kValue;
int minimumComponentSize;
std::filesystem::path path = std::filesystem::u8path(argv[1]);
std::string outputFolder = argv[2];
std::string color = argv[3];

std::stringstream convert{argv[4]};
if (!(convert >> gaussianBlur))
{
     gaussianBlur = 1.5; // default value
}

std::stringstream convertK{argv[5]};
if (!(convertK >> kValue))
{
     kValue = 900; // default value
}

std::stringstream convertMin{argv[6]};
if (!(convertMin >> minimumComponentSize))
{
     minimumComponentSize = 900;
}
 ....

As you can see, I'm creating a stringstream variable for each argument that I want to convert to a numeric type. I can't re-assign another value to stringstream variables. Is there a way to convert all the arguments from a single stringstream ? Is there a better way to do this?

Answer 1

You can write the required argv values into a single stringstream (separated by spaces), then read each out into the corresponding variables:

//...
std::stringstream convert;
convert << argv[4] << " " << argv[5] << " " argv[6]; // Add more "argv" strings
convert >> gaussianBlur >> kValue >> minimumComponentSize; // Read more values
//...

But, of course, error conditions are then a bit trickier to check for; if you need this, you can read the items from that (single) stringstream one at a time, as you already do:

if (!(convert >> gaussianBlur))
{
    gaussianBlur = 1.5; // default value
}
if (!(convert >> kValue))
{
    kValue = 900; // default value
}
if (!(convert >> minimumComponentSize))
{
    minimumComponentSize = 900;
}

Answer 2

To reassign a different value to the same std::stringstream you'll need to clear it:

convert.str(std::string());

Now it's clerared an you can reuse it with a different value.

You must also call convert.clear(); to reset all the previously seted flags.

To add all the arguments to the same std::stringstream @AdrianMole's answer .