/**
 * file: main.c
 * author: 简单教程(www.twle.cn)
 */

#include <stdio.h>

#include <stdlib.h>

int main()
{
   char str1[1024];
   FILE *fptr;

   fptr = fopen("test1.txt", "w");

   if(fptr == NULL)
   {
      printf("Error!");
      exit(1);
   }

   printf("输入字符串:\n");
   fgets(str1, (sizeof str1 / sizeof str1[0]), stdin);

   fprintf(fptr,"%s", str1);
   fclose(fptr);

   return 0;
}

$ gcc main.c && ./a.out
输入字符串:
Hello www.twle.cn ! Hello World

$ cat test1.txt
Hello www.twle.cn ! Hello World