Convert vector of strings to vector of integers in C++

This post will discuss how to convert a vector of strings to a vector of integers in C++.

The std::transform standard algorithm applies an operation to each of the elements in the specified range and returns the result stored in another range. It defined in the <algorithm> header. This post provides an overview of some of the available alternatives to accomplish this with the std::transform algorithm.

1. Using `stoi()` function

Starting with C++11, you can use the stoi function to convert a string to an int, defined in the <string> header file. It throws std::invalid_argument if the string cannot be parsed. However, it can extract the integer value 1 from the strings like 1s.

#include <iostream>

#include <vector>

#include <algorithm>

int main()

{

std::vector<std::string> strings = {"1", "2", "3", "4"};

std::vector<int> ints;

std::transform(strings.begin(), strings.end(), std::back_inserter(ints),

[&](std::string s) {

return stoi(s);

});

for (auto &i: ints) {

std::cout << i << ' ';

}

return 0;

}

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Output:

1 2 3 4

2. Using `boost::lexical_cast`

If you use the boost library in your project, you may use the boost::lexical_cast function for converting a string to an integer.

#include <iostream>

#include <vector>

#include <algorithm>

#include <boost/lexical_cast.hpp>

int main()

{

std::vector<std::string> strings = {"1", "2", "3", "4"};

std::vector<int> ints;

try {

std::transform(strings.begin(), strings.end(), std::back_inserter(ints),

[&](std::string s) {

return boost::lexical_cast<int>(s);

});

}

catch (const boost::bad_lexical_cast &) {

// invalid input - string is not numeric

}

for (auto &i: ints) {

std::cout << i << ' ';

}

return 0;

}

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Output:

1 2 3 4

3. Using String Streams

Another option is to use the string stream to easily convert an integer to a std::string. The following C++ program demonstrates its usage:

#include <iostream>

#include <vector>

#include <algorithm>

#include <sstream>

int main()

{

std::vector<std::string> strings = {"1", "2", "3", "4"};

std::vector<int> ints;

std::transform(strings.begin(), strings.end(), std::back_inserter(ints),

[&](std::string s) {

std::stringstream ss(s);

int i;

ss >> i;

return i;

});

for (auto &i: ints) {

std::cout << i << ' ';

}

return 0;

}

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Output:

1 2 3 4

That’s all about converting a vector of strings to a vector of integers in C++.

Convert vector of strings to vector of integers in C++

1. Using stoi() function

2. Using boost::lexical_cast

3. Using String Streams

1. Using `stoi()` function

2. Using `boost::lexical_cast`