Assigning strings in C

The provided text explains the difference between using a character pointer (char *string) and a character array (char string[]) to store and modify strings in C. Let's rephrase it for clarity and improved flow:

The C code examples demonstrate a crucial distinction between pointers and arrays, often a source of confusion for beginners. Consider these snippets:

Example 1 (Segmentation Fault):

<code class="language-c">#include <stdio.h>
int main(void) {
    char *string = "Wello, world!"; // string is a pointer
    string[0] = 'H';              // Attempting to modify a read-only string
    puts(string);
}</code>

This code results in a segmentation fault. Why? Because string is declared as a pointer to a character. This pointer is initialized to point to a string literal ("Wello, world!"), which is typically stored in read-only memory. Attempting to modify the contents of this read-only memory causes a segmentation fault (a memory access violation).

Example 2 (Successful Modification):

<code class="language-c">#include <stdio.h>
int main(void) {
    char string[] = "Wello, world!"; // string is an array
    string[0] = 'H';              // Modifying a writable copy of the string
    puts(string);
}</code>

This code successfully prints "Hello, world!". Here, string is declared as a character array. The compiler allocates space on the stack to hold a copy of the string literal. This copy is writable, allowing modification of string[0] without causing an error.

The Key Difference:

The fundamental difference lies in how the string is stored. In Example 1, the string literal resides in read-only memory, and the pointer simply points to it. In Example 2, a writable copy of the string literal is created and stored in the array on the stack.

Conclusion:

Pointers and arrays are distinct data types in C. While they may appear similar in some contexts, their behavior can differ significantly, especially when dealing with string literals. Always be mindful of this distinction to avoid unexpected errors and segmentation faults. Using character arrays for modifiable strings is generally safer than using character pointers to string literals.

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