


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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