const变量是否真的不能修改吗？

代码一：

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

char  *my_strnchr( const char  *str, int ch, int which )
{
	int n = 0;
	do
	{
		if( *str == '\0')
		{
			return 0;
		}
		if( *str++ == ch )
			n++; 
	}while( n != which );

    return  str - 1;

}

int main()
{
	printf( "%s\n", my_strnchr( "kkm", 'k', 1) );
	return 0;
}

编译报错：gtk.c:17:5: warning: return discards 'const' qualifier from pointer target type [enabled by default]

代码二：

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

char  *my_strnchr( const char  *str, int ch, int which )
{
	int n = 0;
	do
	{
		if( *str == '\0')
		{
			return 0;
		}
		if( *str++ == ch )
			n++; 
	}while( n != which );

    return  (char*)str - 1;//修改的地方

}


int main()
{
	printf( "%s\n", my_strnchr( "kkm", 'k', 1) );
	return 0;
}

输出完成 (耗时 0 秒) - 正常终止

 

参考连接：

https://blog.youkuaiyun.com/u012780337/article/details/53967143