Different ways to split a string in C++

All high-level programming languages provide a large amount of functions for strings manipulation and splitting is one of the most useful ones. Here are some example of how to perform a string split in Python and C# programming languages:


s = 'Hello world'
result = s.split(' ')

# Result is ['Hello', 'world']


var str = "Hello world";
result = str.Split([' ']);

// Result is ['Hello', 'world']

In C++ there is not such built-in functions to split a string by a delimiter; however, it is possible to write your own split function. There are two approaches though:

In classic C way

In C standard library has a <string.h> header file that provides some useful functions for string manipulation and one of them is strtok.

The strtok() function is used to isolate sequential tokens in a null-terminated string, str. These tokens are separated in the string by at least one of the characters in sep.

#include "string.h"
#include "stdio.h"

char* str = "Hello world";
char* splitted = strtok(str, " ");
while (splitted != NULL) {
    printf("%s", splitted);
    splitted = strtok(NULL, " ");

In the about example, please consider the following description:

The first time that strtok() is called, str should be specified; subsequent calls, wishing to obtain further tokens from the same string, should pass a null pointer instead. The separator string, sep, must be supplied each time, and may change between calls.

Please also note that if you want to use the above code in a C++ application, you should change the include section string.h to <cstring>.

The modern C++ way

The other approach is to use C++11 std::string class. The new string class provides various useful functions to work with strings. However and as far as I know, it doesn’t have any split functions yet. But you can simply create one using other functions provided in the string class. The following is an implementation of split function in C++:

#include <string>
#include <vector>

std::vector<std::string> split(const std::string &str, const std::string &delim)
    std::vector<std::string> tokens;
    size_t prev = 0, pos = 0;
        pos = str.find(delim, prev);
        if (pos == std::string::npos)
            pos = str.length();
        std::string token = str.substr(prev, pos - prev);
        if (!token.empty())
        prev = pos + delim.length();
    } while (pos < str.length() && prev < str.length());
    return tokens;

As you can see in the above code, we have used the built-in find and substr functions to implement our own split! Finally we pushed each token to a vector and return it to the user. The reason we have used the vector is because we don’t know how many items would be in our result list.

11 Feb 2020