用C语言实现从文本文件中读取数据后进行排序的功能

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

/*=============================
  制作于：Aug 16, 2016
  by QQ:1729403632
===============================*/

#define ST 64 //字符串大小

void mergesort(int *, int);
void _mergesort(int *, int, int, int *);
void merge(int *, int, int, int, int *);
char * s_gets(char *, int);

int main(int argc, char * argv[]){
  FILE * sor, * dest; //sor源文件 dest目标文件
  int * ptr;//临时数组
  int i, n; //n表示元素个数
  char fname[ST]; //临时存储字符串

  printf("请输入元素个数:");
  while( scanf("%d", &n) != 1 || n <= 0 ){
    printf("输入错误,请重新输入！\n");
    while(getchar() != '\n')
      continue;
  }
  while(getchar() != '\n')
      continue;

  ptr = (int *)malloc( (size_t)n * sizeof(int) ); //申请动态数组//////
  if(ptr == NULL){
    fprintf(stderr, "FAIL TO ASK FOR MEMORY SPACE\n");
    exit(EXIT_FAILURE);
  }

  printf("请输入原文件名:");
  if( s_gets(fname, ST) == NULL ){
    fprintf(stderr, "Fail to get a string\n");
    exit(EXIT_FAILURE);
  }

  sor = fopen(fname, "r"); //打开包含数据的源文件
  if(sor == NULL){
    fprintf(stderr, "Fail to open the source file\n");
    exit(EXIT_FAILURE);
  }

  for(i = 0; i < n; i++) //获取数据到动态数组
    if( fscanf(sor, "%d", &ptr[i]) != 1 ){
      fprintf(stderr, "Fail to get the data\n");
      exit(EXIT_FAILURE);
    }

  mergesort(ptr, n); //排序

  printf("请输入要保存数据的文件名：");
  if( s_gets(fname, ST) == NULL ){
    fprintf(stderr, "Fail to get a string\n");
    exit(EXIT_FAILURE);
  }

  dest = fopen(fname, "w"); //打开目标文件
  if(dest == NULL){
    fprintf(stderr, "Fail to open the destination file\n");
    exit(EXIT_FAILURE);
  }

  for(i = 0; i < n; i++){ //输出数据到目标文件
    if( fprintf(dest, "%d\t", ptr[i]) < 0 ){
      fprintf(stderr, "Fail to save the data\n");
      exit(EXIT_FAILURE);
    }
    if( ((i + 1) % 10) == 0){ //如果写满10个就换行
      if( fprintf(dest, "\n") < 0 ){
        fprintf(stderr, "Fail to save the data\n");
        exit(EXIT_FAILURE);
      }
    }
  }

  if( fclose(sor) != 0 ){ //关闭源文件
    fprintf(stderr, "Fail to close the source file\n");
    exit(EXIT_FAILURE);
  }
  if( fclose(dest) != 0 ){ //关闭目标文件
    fprintf(stderr, "Fail to close the destination file\n");
    exit(EXIT_FAILURE);
  }
  free(ptr); //释放内存

  printf("成功完成！\n请按任意键继续^ ^\b\b");

  getch();
  return 0;
}

void mergesort(int * ar, int size){
  if(size > 0){
    int * temp;
    temp = (int *)malloc( (size_t)size * sizeof(int) ); /////
    if(temp == NULL){
      fprintf(stderr, "Fail to ask for MEMORY SPACE\n");
      exit(EXIT_FAILURE);
    }
    _mergesort(ar, 0, size - 1, temp); //归并排序
    free(temp);
  }
}

void _mergesort(int * ar, int start, int end, int * temp){
  if(start < end){
    int mid = (start + end) / 2;
    _mergesort(ar, start, mid, temp);  //左子数组排序
    _mergesort(ar, mid + 1, end, temp);  //右子数组排序
    merge(ar, start, mid, end, temp);  //合并子数组
  }
}

void merge(int * ar, int p, int q, int r, int * temp){
  int i = p, j = q + 1, k = 0;
  while(i <= q && j <= r){
    if(ar[i] < ar[j])
      temp[k++] = ar[i++];
    else
      temp[k++] = ar[j++];
  }
  while(i <= q)  //如果序列[i...q]存在，追加
    temp[k++] = ar[i++];
  while(j <= r)  //如果序列[j...r]存在，追加
    temp[k++] = ar[j++];

  for(k = 0; k <= (r - p); k++)
    ar[p + k] = temp[k];
}

char * s_gets(char * st, int size){
  char * re;
  int i = 0;

  re = fgets(st, size, stdin);
  if(re){
    while(st[i] != '\n' && st[i] != '\0') //如果没有到输入字符串结束
      i++;  //递增
    if(st[i] == '\n') //如果字符串最后一个字符是'\n'
      st[i] = '\0'; //把它变成'\0'
    else //否则缓冲区内还有一部分超出读取范围的字符没有被读取
      while(getchar() != '\n') //把这些字符读取完（清空缓冲区）
        continue;
  }

  return re;
}