Strings

Strings#

reading

std::string on cplusplus.com

A string is a sequence of characters and is how we represent text in a computer program.

Character vs string#

In C++, there is a distinction between a single character and a string.

Single quotes, 'x' are used to hold a single character. This will have the datatype char, e.g.,
```
char c = 'x';
```
A char is typically a single byte, and therefore can represent 256 values. Traditionally, the ASCII encoding was used.

An alternate encoding, Unicode can represent > 1 million characters, but cannot fit in a single char.
Double quotes, "This is a string" hold a collection of characters—what we call a string. This uses the datatype std::string, e.g.,
```
#include <string>

std::string s = "This is a string";
```

Warning

C++ can also use older C-style strings, which are essentially a null-terminated array of characters, e.g.,

char c_string[] = "This is my string";

These are quite inflexible and can lead to coding errors if you are not careful, and we will avoid them as much as possible.

`std::string`#

A C++ std::string holds a sequence of characters. When working with strings, we include the <string> header.

Here’s a first example. We’ll create a string and output it to the screen:

Listing 18 string_example.cpp#

#include <iostream>
#include <string>

int main() {

    std::string example{"This is PHY 504"};

    std::cout << example << std::endl;
}

We can use a constructor to create an initial string filled with a character repeated many times. For instance, here’s an 80-character line:

Listing 19 string-repeat.cpp#

#include <iostream>
#include <string>

int main() {

    std::string line(80, '-');

    std::cout << line << std::endl;

}

We’ll learn more about constructors when we discuss classes in C++.

Here, '-' is a char and not a string.

Note

A nice overview of working with C++ strings is provided by “hacking C++”: std::string

A C++ string is a collection of bytes (char) and on many operating systems will be Unicode (UTF-8 encoding). For example, we could do:

#include <string>

std::string greek = "αβγδεζηθικλμνξοπρστυφχψω";

Tip

By default, when we create a string, it is initialized to be empty, so we don’t need to do:

std::string a{};

but instead can just do:

std::string a;

Escape sequences#

There are some important special characters that we don’t type directly, but instead we precede with a \. For instance, to add a new line to a string, we can use \n.

Note

\n is slightly different than std::endl—the latter also flushes the output buffer.

Here’s a list of escape sequences.

try it…

Let’s try the “bell”, \a, to see if it has an effect on our terminal.

String math#

There are a lot of operators and functions that can work on strings. See https://en.cppreference.com/w/cpp/string/basic_string.html

We can concatenate strings using the + operator:

Listing 20 string-cat.cpp#

#include <iostream>
#include <string>

int main() {

    std::string a{"this is a test"};
    std::string b{"of concatenation"};

    std::cout << a + " " + b << std::endl;

}