c - strncpy 函数无法正常工作

Question

我想做的是要求用户输入以下格式的内容:cd 目录。然后我将“cd”存储在一个字符串中，将“directory”存储在另一个字符串中。这是我的代码:

void main()
{
   char buf[50], cdstr[2], dirstr[50];

   printf("Enter something: ");
   fgets(buf, sizeof(buf), stdin);

   //store cd in cdstr
   strncpy(cdstr, buf, 2);
   printf("cdstr: %s(test chars)\n", cdstr);

   //store directory in dirstr
   strncpy(dirstr, buf+3, sizeof(buf)-3);
   printf("dirstr: %s(test chars)\n", dirstr);
}

输出如下，输入为:cd 路径名

cdstr: cdcd pathname  //incorrect answer
(test chars)          //an extra "\n"
dirstr: pathname      //correct answer
(test chars)          //an extra "\n" 

这就是为什么？

Answer 1

这是因为做了strncpy(cdstr, buf, 2)之后， cdstr 中没有以 NULL 结尾的字符串char大批。您可以通过更改 cdstr 来修复它长度为 3 并添加:cdstr[2] = '\0' :

void main()
{
   char buf[50], cdstr[3], dirstr[50]={0};

   printf("Enter something: ");
   fgets(buf, sizeof(buf), stdin);

   //store cd in cdstr
   strncpy(cdstr, buf, 2);
   cdstr[2] = '\0';
   printf("cdstr: %s(test chars)\n", cdstr);

   //store directory in dirstr
   strncpy(dirstr, buf+3, sizeof(buf)-3);
   printf("dirstr: %s(test chars)\n", dirstr);
}