Extracting value from a vector in C++

Question

I have a vector that consists of an array of data after reading in a config file. Now, I will like to extract some values in the vector and passing it as int. I am able to get the value range but I am not sure how to continue from there on.

Example:

string MapXInput, MapYInput; vector <string> placeholder; cout << placeholder[0] << endl; // will cout MapXInput=12-20 cout << placeholder[1] << endl; // will cout MapYInput=13-19 MapXInput = placeholder[0].substr(10, 99); // will extract 12-20 MapYInput = placeholder[1].substr(10, 99); // will extract 13-19 int x_start, x_end; int y_start, y_end; ... // from here on, unsure how to proceed // x_start is suppose to obtain '12' and turn it into int // x_end is suppose to obtain '20' and turn it into int // y_start is suppose to obtain '13' and turn it into int // y_end is suppose to obtain '19' and turn it into int

Note that MapXInput= and MapYInput= will always be fixed in the config file. The range value is changeable depending on the user input. I tried this:

int x_start = stoi(MapXInput[1]);

But it produce the error

no matching function for call to 'stoi(char&)'

End result suppose to be:

x_start = 12 x_end = 20 y_start = 13 y_end = 19

What is the approach?

Tony Delroy · Accepted Answer · 2020-07-19 03:33:41Z

An easy approach is to use a std::istringstream:

std::istringstream iss{MapXInput}; // e.g. "12-20" char c; if (!(iss >> x_start >> c >> x_end && c == '-')) { std::cerr << "unable to parse MapXInput\n"; exit(EXIT_FAILURE); }

You can think of iss >> x_start >> c >> x_end as meaning "can I parse/extract 3 values of values of whatever types x_starts, c and x_end are. && is the logical AND operator in C++. c == '-' checks the character between the ints was a hyphen. ! is the logical NOT operator, and therefore the if conditions handles cases where parsing fails or the separator is not '-'. You could other conditions in there, such as range checks on the integer values.

Cool, it worked. Just went to read up on istringstream and didn't know this exist (I am new to C++). By the way, when I check the datatype for my x_start, it output the typeid of 'i'. I suppose this is an integer datatype?
@user3118602 -- Apart from iss and c, Tony Delroy used the variables that you declared them in your post.
Got it, just want to make sure it is an integer datatype! Thanks!

Darian Lopez Utra · Accepted Answer · 2020-07-19 03:09:43Z

Splitting a string by a character. this should do the trick:

std::stringstream test("this_is_a_test_string"); std::string segment; std::vector<std::string> seglist; while(std::getline(test, segment, '_')) { seglist.push_back(segment); }

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