c - pointer is also pass by value

最新推荐文章于 2022-06-16 15:05:14 发布

最新推荐文章于 2022-06-16 15:05:14 发布 · 134 阅读

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本文详细解析了C语言中使用指针作为函数参数时的传值机制，包括如何通过地址修改指向的值，但不能直接修改指针本身，以及如何通过返回新地址来实现对外部变量的改变。通过实例代码演示了这些概念的应用。

c - pointer is also pass by value

when pointer as param of function, it is also pass by value:

* you can change the value that the pointer point to by the address(the value of pointer),

* but you can't change the original value of pointer in the function,

* if you want to change the pointer, you need to return the new address from function, and assign it to the pointer outside the function,

e.g.

pass_by_value.c:

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

char *test(char *s) {
	s = strdup("s2");
	return s;
}

main() {
	char *s1;
	s1 = "s1";
	printf("%s\n", s1);	// s1
	
	test(s1);
	printf("%s\n", s1);	// s1, because pointer param of function is also pass by value, you can't change the original value of pointer in the function, even though you can change the value it point to by the address(the value of pointer).
	
	s1 = test(s1);
	printf("%s\n", s1);	// s2, because new address is returned from function, and assign to pointer outside the function.
}