Parsing and turning a string into a number

Question

I have an input file which I'm reading in with the basic myFile >> variable since I know the format and the format will always be correct. The file I'm reading in is formatted as instruction <num> <num> and to make >> work, I'm reading everything in as a string. If I have 3 variables, one to take in each piece of the line, how can I then turn string <1> (for example) into int 1? I know the string's first and last characters are brackets which need to be removed, then I could cast to an int, but I'm new to C++ and would like some insight on the best method of doing this (finding and removing the <>, then casting to int)

possible duplicate of [Parse (split) a string in C++ using string delimiter (standard C++)](http://stackoverflow.com/questions/14265581/parse-split-a-string-in-c-using-string-delimiter-standard-c) — ha9u63a7, Mar 18 '15 at 21:09

score 1 · Answer 1 · answered Mar 18 '15 at 21:16

1

use stringstream

#include <string>
#include <sstream>
#include <iostream>

int main() {
    std::string str = "<1>";
    int value;
    std::stringstream ss(str);
    char c;

    ss >> c >> value >> c;

    std::cout << value;
}

answered Mar 18 '15 at 21:16

olive007

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got it, this works, initially I had `value` as a string and it wasn't getting rid of the last `>`, but I changed it and it works. Thanks! – Tommy K Mar 18 '15 at 21:24

score 0 · Answer 2 · answered Mar 18 '15 at 21:11

0

First to get the middle character out you can just do char myChar = inputString.at(1);. Then you can do int myInt = (int)myChar;

answered Mar 18 '15 at 21:11

Nicholas Callahan

153
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Incorrect, and also using C-style casts. The stringstream answer above is better, and can also be wrapped in a templated function. – Erik Alapää Mar 18 '15 at 21:18
it won't always be a one-digit number though. I'm trying to use .erase() on the string to get rid of the first and last iterator to erase the <> but its not working as I expected. – Tommy K Mar 18 '15 at 21:18

score 0 · Answer 3 · answered Mar 18 '15 at 21:15

Even if you remove the <> characters, your still importing the file content into a string using >> so you still need to cast it to an int. If you have only 1 value, you can follow what Nicholas Callahan wrote in the previous answer, but if you have multiple characters you want to read as int, you dont have a choice but to cast.

score 0 · Answer 4 · answered Mar 18 '15 at 21:22

0

You can also resort to sscanf.

#include <cstdio>
#include <iostream>
#include <string>

int main()
{
    std::string str = "<1234>";
    int value;
    sscanf(str.c_str(), "<%d>", &value);
    std::cout << value << std::endl;
}

answered Mar 18 '15 at 21:22

R Sahu

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14
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270

Parsing and turning a string into a number

4 Answers4