C编程:获取行、二维数组和结束用户输入

Question

char* str = NULL;
size_t capacity = 0;

getline(&str, &capacity, stdin); 

上面的代码是在读取字符串输入时使用getline动态分配内存的示例。但是，如果我试图将输入读取到一个二维数组中，该怎么办？

示例：

Linenumberone (enter)
Linenumbertwo (enter)
(enter) <<< enter on an empty line - stop reading user input

我确实知道strlen函数，所以我想我可以从技术上使用它来确定何时停止读取用户输入？但我有点困惑，是否可以使用getline将用户输入读取到C中的二维数组中？我只看到人们在C++中使用它

Answer 1

我们可以声明一个指针数组，然后在循环中将每一行赋给2D数组。请参见以下代码：

#include <stdio.h>
#include <stdlib.h>

int main()
{
    char *line[5] = {NULL}; // array of 5 pointers
    size_t len = 0;

    int i=0;

    for(i=0;i<5;i++)
    {
        getline(&line[i],&len, stdin); // reading strings
    }
    
    printf("\nThe strings are \n");
    for(int i=0; i<5; i++)
    {
        printf("%s",line[i]);  // prinitng the strings.
    }


    return 0;
}

输出为(输入前5行)：

krishna
rachita
teja 
sindhu
sagarika

The strings are 
krishna
rachita
teja 
sindhu
sagarika

Answer 2

每次使用characters = getline(&str,...)时，都会在地址str处分配新的动态内存，其大小等于characters读取次数。在每次getline()调用时，将缓冲区地址(str的值)存储到一个数组中就足够了。随后，getline()中的缓冲区地址(str)会递增上一个getine()中读取的字符数。请参阅下面的代码和示例。

#include <stdio.h>

int main () {
  char *buffer=NULL;
  size_t capacity = 0;
  size_t maxlines = 100;
  char *lines[maxlines]; // pointers into the malloc buffer for each line

  printf ("Input\n\n");

  int lines_read;
  int characters;
// read getline until empty line or maxlines
  for (lines_read = 0; lines_read < maxlines; lines_read++)  {
      printf ("Enter line %d: ", lines_read + 1);
      characters = getline (&buffer, &capacity, stdin);
// stop at empty line
      if (characters == 1) break;
// convert end of line "\n" into zero (C null-terminated string convention)
      buffer[characters - 1] = 0;
// save starting location into lines
      lines[lines_read] = buffer; // save pointer to the start of  this line in the buffer
      buffer += characters;       // set  pointer to the start of a new line in the buffer
  }

  printf ("\nOutput\n\n");

  // print lines read excluding empty line
  for (int i = 0; i < lines_read; i++)
    printf ("Line[%d] = %s\n", i+1, lines[i]);

  return (0);
}

输出示例：

Input

Enter line 1: This
Enter line 2: is
Enter line 3: an
Enter line 4: example.
Enter line 5: 

Output

Line[1] = This
Line[2] = is
Line[3] = an
Line[4] = example.