c/c++指针常见错误

一

#include <bits/stdc++.h>
using namespace std;
void f(char *str)
{
    char *s = str;
    str[0] = '0' //error str是指向常量的指针，只能读取不能修改,如果str是malloc过则可以修改
    s[1] = '1'; //同上error
    cout<<s<<endl;
}
int main()
{
    char *s = "We Are Happy.";
    f(s);
    puts(s);
    return 0;
}

二

#include <bits/stdc++.h>
using namespace std;
void f(char *str)
{
    char *s = str;
    s[0] = 'a', s[1] = 'b', s[2] = 'c', s[3] = '\0';
    str = s;
}
int main()
{
    char s[] = "We Are Happy.";
    f(s);
    puts(s); //abc
    return 0;
}

三

#include <bits/stdc++.h>
using namespace std;
void f(char *str)
{
    char *s = (char *)malloc(sizeof(char)*100);
    s[0] = 'a', s[1] = 'b', s[2] = 'c', s[3] = '\0';
    str = s; //局部变量不会影响主函数
}
int main()
{
    char s[] = "We Are Happy.";
    f(s);
    puts(s);    //We Are Happy.
    return 0;
}

 

四

#include <bits/stdc++.h>
using namespace std;
void f(char *str)
{
    char *s = (char *)malloc(sizeof(char)*100);
    s[0] = 'a', s[1] = 'b', s[2] = 'c', s[3] = '\0';
    strcpy(str, s); //将s内的元素赋值给str，改变的不是指针是指针指向的值
}
int main()
{
    char s[] = "We Are Happy.";
    f(s);
    puts(s);    //abc
    return 0;
}