用fopen函数创建或打开一个文本文件，并写入字符串“this is a test file.

#include<stdio.h>
void main()
{
 FILE *fptr;
 if((fptr=fopen("test.txt","w"))!=NULL)
 {
  fprintf(fptr,"this is a test file.");
  fclose(fptr);
 }
 else
  printf("error");
}