c - C中的二维数组

Question

我需要在一个二维数组中维护五个学生的名字。每个学生姓名的长度可以为 20 个字符。如果第六个学生条目出现，则第一个将被替换，第七个将替换第二个，依此类推。

下面是我的程序。当我为第二个学生调用 set 函数(在二维数组中添加学生记录)时，请告诉我为什么我的第一个学生记录被替换。

我根据您的建议更新了代码，但仍然无济于事。请提出建议。

#include <stdio.h>
#include<strings.h>

void display(char s[][21]);

void set(char stuName[][21],char* merchantNo)
{

        for(int i = 0;i<5;i++)
        {
                if(stuName[i][21] == '\0')
                {
                        strcpy(stuName[i], merchantNo);
                        break;
                }
        }
}

void display(char s[][21])
{
    for(int i = 0;i<5;i++)
        {
        printf("s[%d] is [%s]\n",i,s[i]);
        }
}

int main()
{
        char stuName[5][21];

        printf("sizeof(stuName) is [%d]\n",sizeof(stuName));

        memset(stuName,'\0',sizeof(stuName));

        display(stuName);

        set(stuName,"Student1");
        display(stuName);

        set(stuName,"Student2");

        display(stuName);

        return 0;
}

输出

s[0] is []
s[1] is []
s[2] is []
s[3] is []
s[4] is []
s[0] is [Student1]
s[1] is []
s[2] is []
s[3] is []
s[4] is []
s[0] is [Student2]
s[1] is []
s[2] is []
s[3] is []
s[4] is []

Answer 1

看起来您需要将您的 set 函数修改为:

int set(char stuName[][21], char* merchantNo)
{
    int l = strlen(merchantNo);
    if (21 <= l) // input name is greater than your array
       return -1;

    for (int i = 0; i < 5; i++)
    {
        if (stuName[i][0] == '\0')
        {
            strncpy(stuName[i], merchantNo, l);
            return i; // return the position where you've added
        }
    }
    return -2;  // array full, can't add new entry
}