Constant Strings in C

String Literals

A string literal is a sequence of characters enclosed in double quotes. When used to initialize a character array, it creates a constant string.

In this example, greeting is a pointer to a constant string. The const keyword indicates that the string is read-only, and attempting to modify it may result in undefined behavior.

Characteristics of Constant Strings

1. Read-Only:

   • String literals are read-only by default.

   • Modifying the characters of a string literal is undefined behavior.

2. Storage in Read-Only Memory:

   • String literals are often stored in read-only memory.

   • Attempting to modify a string literal can lead to a runtime error.

3. Initialization at Compile Time:

   • String literals are typically initialized at compile time.

Usage of Constant Strings

Constant strings are commonly used for:

• Message Printing:

  printf("Error: File not found\n");

• Function Parameters:

  void printMessage(const char *message) { printf("%s\n", message); }

• Array Initialization:

  const char vowels[] = {'a', 'e', 'i', 'o', 'u', '\0'};

• Command-Line Arguments:

  int main(int argc, const char *argv[]) { // Access command-line arguments // ... }

Modification Attempts

Attempting to modify a constant string can lead to unexpected behavior. The following code is incorrect:

To avoid this, it's recommended to use character arrays for strings that need to be modified:

Conclusion

Constant strings, defined as string literals, play a crucial role in C programming for representing read-only text. Understanding their characteristics and adhering to the read-only nature is essential for writing robust and error-free C code.

If you have specific questions or if there are additional topics you'd like to explore, feel free to ask!