# C++ Split a String by a Multi-Character Delimiter

> Split a C++ string on a multi-character delimiter using string::find and string::substr in a loop, since the standard library has no built-in split function

**URL:** https://sentry.io/answers/split-string-in-cpp/

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## The Problem

Imagine you're building a web service that requires you to store each word from a URL query. Your input string will have spaces represented by their HTML encoding, `%20`, like so:

```C++
#include <iostream>
#include <vector>

using namespace std;

vector<string> getWords(string s) {
    //YOUR CODE HERE
}

int main() {
    string s = "This%20is%20a%20string.";
    for (string x: getWords(s)) {
        cout << x << endl;
    }
    return 0;
}
```

There is no standard `split()` function in C++ like there is in other languages such as Python and JavaScript, so how can you split a string in C++ using a string delimiter?

## The Solution

There are several fairly simple methods one can implement to solve this problem, each with pros and cons.

The `getline()` function is a simple and more readable solution whenever you need to split a string by a character and not a string of length > 1.

The `strtok()` function uses a static buffer to enable a fairly simple (albeit slightly less intuitive) implementation. Unlike `getline()`, `strtok()` supports a delimiter of type `string`, which seems to make this function a viable solution. However, while a string can be supplied as the delimiter to `strtok()`, the function interprets it as meaning "split the input by *every character in the delimiter string*".

Since the question specifies that the delimiter must itself be a string, the recommended way to approach this problem would be to use `string.find()` and `string.substr()`.

### Use `string.find()` and `string.substr()`

For this method, we need to include the string library:

```C++
#include <string>
```

The `string.find()` function has the following signature:

```C++
string.find(string delim)
```

It returns the index of the first character of the delimiter within the string from which `find()` is called.

The `string.substr()` function has the following signature:

```C++
string.substr(size_t begin, size_t length)
```

It returns the substring of `string` that begins at index `begin` and has length `length`.

These two functions can be used together, like so:

```C++
#include <string>

vector<string> getWords(string s){
    vector<string> res;
    int pos = 0;
    while(pos < s.size()){
        pos = s.find("%20");
        res.push_back(s.substr(0,pos));
        s.erase(0,pos+3); // 3 is the length of the delimiter, "%20"
    }
    return res;
}
```

```
This
is
a
string.
```

This method treats the delimiter as a proper string, so if the input string is:

```C++
string s = "This%20is%20a%20str2ing.";
```

Then the output will be:

```
This
is
a
str2ing.
```

Note here that, although we erase `s` from the input string at each iteration, we pass the string by value and thus make a copy that we can destroy without affecting the original string.

### Build Your Own

Of course, if you have an objection to using prebuilt functions altogether, you could always build your own method for splitting a string. Here is one example of how you might implement it:

```C++
vector<string> getWords(string s) {
    vector<string> res;
    string delim = "%20";
    string token = "";
    for (int i = 0; i < s.size(); i++) {
        bool flag = true;
        for (int j = 0; j < delim.size(); j++) {
            if (s[i + j] != delim[j]) flag = false;
        }
        if (flag) {
            if (token.size() > 0) {
                res.push_back(token);
                token = "";
                i += delim.size() - 1;
            }
        } else {
            token += s[i];
        }
    }
    res.push_back(token);
    return res;
}
```

Output:

```
This
is
a
str2ing.
```

### Further Reading

- [`std::ranges::views::split`](https://en.cppreference.com/w/cpp/ranges/split_view.html) — a C++20 ranges-based alternative that splits any range, including strings, without writing a loop

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*Source: [sentry.io/answers/split-string-in-cpp/](https://sentry.io/answers/split-string-in-cpp/)*