A must-have for veterans: Tips and precautions for * and & in C language

In C language, it represents a pointer, which stores the address of other variables; & represents the address operator, which returns the memory address of the variable. Tips for using pointers include defining pointers, dereferencing pointers, and ensuring that pointers point to valid addresses; tips for using address operators & include obtaining variable addresses, and returning the address of the first element of the array when obtaining the address of an array element. A practical example demonstrating the use of pointer and address operators to reverse a string.

* and & in C language: Tips and precautions

Introduction

Pointer () and address operator (&) are powerful tools in C language that can manipulate memory addresses and data. Understanding its usage is crucial, especially for experienced developers. This article will delve into the techniques and precautions of and &, and provide practical cases to illustrate their usage.

Pointer (*)

• Pointer is a variable that stores the address of other variables.
• Use the * operator to define a pointer: int *ptr = &var; (store the address of var in the pointer ptr)
• Use the * operator to dereference the pointer: *ptr(Access the value stored in ptr)

Note:

• Make sure the pointer points to valid memory address, otherwise a segfault may occur.
• Before using a dereferenced pointer, make sure it is not NULL.
• Prevent wild pointers (pointers that do not point to valid addresses).

Address operator (&)

• The address operator returns the memory address of a variable.
• Use the & operator to get the address of a variable: int *ptr = &var;
• & operator can be used to initialize a pointer.

Note:

• Only the address of an addressable object (such as a variable) can be obtained.
• When obtaining the address of an array element, the & operator returns the address of the first element of the array, not the address of the actual element.

Practical case

Reversal of string

#include <stdio.h>
#include <string.h>

void reverse_string(char *str) {
  int len = strlen(str);
  int i;

  for (i = 0; i < len / 2; i++) {
    char temp = str[i];
    str[i] = str[len - i - 1];
    str[len - i - 1] = temp;
  }
}

int main() {
  char str[] = "Hello world";
  reverse_string(str);
  printf("%s", str);  // 输出：dlrow olleH
  return 0;
}

Conclusion

Mastering the usage of * and & in C language is crucial for advanced programming. By understanding these tips and considerations, developers can effectively manipulate memory addresses and data, improving the efficiency and security of their code.

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