fig23_16.c

来自「经典vc教程的例子程序」· C语言 代码 · 共 171 行

/* This program reads a random access file sequentially, *
 * updates data already written to the file, creates new *
 * data to be placed in the file, and deletes data       *
 * already in the file.                                  */

#include <stdio.h>

struct clientData {
   int acctNum;
   char lastName[15];
   char firstName[10];
   float balance;
};

int enterChoice(void);
void textFile(FILE *);
void updateRecord(FILE *);
void newRecord(FILE *);
void deleteRecord(FILE *);

main()
{
   FILE *cfPtr;
   int choice;

   if ((cfPtr = fopen("credit.dat", "r+")) == NULL)
      printf("File could not be opened.\n");
   else {

      while ((choice = enterChoice()) != 5) {

         switch (choice) {
            case 1:
               textFile(cfPtr);
               break;
            case 2:
               updateRecord(cfPtr);
               break;
            case 3:
               newRecord(cfPtr);
               break;
            case 4:
               deleteRecord(cfPtr);
               break;
         }

      }
   }

   fclose(cfPtr);
   return 0;
}

void textFile(FILE *readPtr)
{
   FILE *writePtr;
   struct clientData client;

   if ((writePtr = fopen("accounts.txt", "w")) == NULL)
      printf("File could not be opened.\n");
   else {
      rewind(readPtr);
      fprintf(writePtr, "%-6s%-16s%-11s%10s\n", 
              "Acct", "Last Name", "First Name","Balance");

		fread(&client, sizeof(struct clientData), 1, readPtr);

		while (!feof(readPtr)) {

			if (client.acctNum != 0)
				fprintf(writePtr, "%-6d%-16s%-11s%10.2f\n",
						  client.acctNum, client.lastName,
						  client.firstName, client.balance);

         fread(&client, sizeof(struct clientData), 1, readPtr);
      }
   }

   fclose(writePtr);
}

void updateRecord(FILE *fPtr)
{
   int account;
   float transaction;
   struct clientData client;

   printf("Enter account to update (1 - 100): ");
   scanf("%d", &account);
   fseek(fPtr, (account - 1) * sizeof(struct clientData), 
         SEEK_SET);
   fread(&client, sizeof(struct clientData), 1, fPtr);

   if (client.acctNum == 0)
      printf("Acount #%d has no information.\n", account);
   else {
      printf("%-6d%-16s%-11s%10.2f\n\n", 
             client.acctNum, client.lastName, 
             client.firstName, client.balance);
      printf("Enter charge (+) or payment (-): ");
      scanf("%f", &transaction);
      client.balance += transaction;
      printf("%-6d%-16s%-11s%10.2f\n", 
             client.acctNum, client.lastName, 
             client.firstName, client.balance);
      fseek(fPtr, (account - 1) * sizeof(struct clientData), 
            SEEK_SET);
      fwrite(&client, sizeof(struct clientData), 1, fPtr);
   }
}

void deleteRecord(FILE *fPtr)
{
   struct clientData client, blankClient = {0, "", "", 0};
   int accountNum;

   printf("Enter account number to delete (1 - 100): ");
   scanf("%d", &accountNum);
   fseek(fPtr, (accountNum - 1) * sizeof(struct clientData), 
         SEEK_SET);
   fread(&client, sizeof(struct clientData), 1, fPtr);

   if (client.acctNum == 0)
      printf("Account %d does not exist.\n", accountNum);
   else {
      fseek(fPtr, (accountNum - 1) * sizeof(struct clientData), 
            SEEK_SET);
      fwrite(&blankClient, sizeof(struct clientData), 1, fPtr);
   }
}

void newRecord(FILE *fPtr)
{
   struct clientData client;
   int accountNum;
   printf("Enter new account number (1 - 100): ");
   scanf("%d", &accountNum);
   fseek(fPtr, (accountNum - 1) * sizeof(struct clientData), 
         SEEK_SET);
   fread(&client, sizeof(struct clientData), 1, fPtr);

   if (client.acctNum != 0)
      printf("Account #%d already contains information.\n",
             client.acctNum);
   else {
      printf("Enter lastname, firstname, balance\n? ");
      scanf("%s%s%f", &client.lastName, &client.firstName, 
            &client.balance);
      client.acctNum = accountNum;
      fseek(fPtr, (client.acctNum - 1) * 
            sizeof(struct clientData), SEEK_SET);
      fwrite(&client, sizeof(struct clientData), 1, fPtr);
   }
}

int enterChoice(void)
{
   int menuChoice;

   printf("\nEnter your choice\n"
          "1 - store a formatted text file of acounts called\n"
          "    \"accounts.txt\" for printing\n"
          "2 - update an account\n"
          "3 - add a new account\n"
          "4 - delete an account\n"
          "5 - end program\n? ");
   scanf("%d", &menuChoice);
   return menuChoice;
}