Strings in C

A string in C is an array of characters terminated by a null character '\0'.

• The null character '\0' marks the end of the string.
• C does not have a built-in string data type.
• Strings are implemented using arrays of char.

The string is: Geeks

• char str[] = "Geeks"; This line declares a character array str and initializes it with the string "Geeks". Internally, this creates an array like: { 'G', 'e', 'e', 'k', 's', '\0'}
  The null character '\0' is automatically added at the end to terminate the string.
• printf("The string is: %s\n", str); %s is the format specifier used to print a string. printf starts at the memory location of str and prints each character until it finds the terminating null character '\0'.

Accessing Characters

We can access any character of the string by providing the index (position) of the character, like in array.

G

Update

We can change individual characters of a string using their index: str[0] = 'h'. Strings can also be updated using standard library functions like strcpy() to replace the entire string. Ensure the new string fits within the allocated array size to avoid memory issues.

R

String Length

To find the length of a string in C, you need to iterate through each character until you reach the null terminator '\0', which marks the end of the string. This process is handled efficiently by the strlen() function from the C standard library.

5

In this example, strlen() returns the length of the string "Geeks", which is 5, excluding the null character.

C language also provides several other useful string library functions to perform operations like copying, comparing, and concatenating strings. You can refer to standard string functions for more details.

String Input

In C, reading a string from the user can be done using different functions, and depending on the use case, one method might be chosen over another. Below, the common methods of reading strings in C will be discussed, including how to handle whitespace, and concepts will be clarified to better understand how string input works.

Using scanf()

The simplest way to read a string in C is by using the scanf() function.

Output

Geeks (Enter by user)
Geeks

In the above program, the string is taken as input using the scanf() function and is also printed. However, there is a limitation with the scanf() function. scanf() will stop reading input as soon as it encounters a whitespace (space, tab, or newline).

Using scanf() with a Scanset

We can also use scanf() to read strings with spaces by utilizing a scanset. A scanset in scanf() allows specifying the characters to include or exclude from the input.

Output

Geeks For Geeks (Enter by user)
Geeks For Geeks

Using fgets()

If someone wants to read a complete string, including spaces, they should use the fgets() function. Unlike scanf(), fgets() reads the entire line, including spaces, until it encounters a newline.

Output

Geeks For Geeks (Enter by user)
Geeks For Geeks

Passing Strings to Function

As strings are character arrays, we can pass strings to functions in the same way we pass an array to a function. Below is a sample program to do this: 

GeeksforGeeks

Strings and Pointers in C

Similar to arrays, In C, we can create a character pointer to a string that points to the starting address of the string which is the first character of the string. The string can be accessed with the help of pointers as shown in the below example.

Geeks

So far, we've seen how to declare and use strings as character arrays. But in C, strings can also be represented using string literals, which offer a simpler way to initialize strings directly in the code. Let's understand what string literals are and how they work.

Strings Literals

A string literal is a sequence of characters enclosed in double quotes, like "Hello" or "1234". Internally, it is stored as a constant character array terminated by a null character '\0'.

Hello World

• "Hello World" is a string literal. It is stored in a read-only section of memory.
• const char *str = "Hello World";
  This creates a pointer to the string literal. Using const is important because string literals should not be modified.
• printf("%s\n", str); prints the string starting from the address stored in str.

Key Points

• String literals are automatically null-terminated.
• They are typically stored in read-only memory, so modifying them causes undefined behavior.
• You can assign string literals to char*, but it's recommended to use const char* for safety.