如何從文件讀取數據？

Question

我正在嘗試創建在c中具有五個功能的電話簿。 我已經形成了第一個功能，該功能需要並保存文件人的知識。 但是，我無法通過第二功能從文件中僅搜索一個人（不是所有人）的知識。

要運行此功能（““ display（）函數”“），我想搜索用戶的名稱並在屏幕上顯示該名稱的知識。 我寫了一些東西，但是沒有用。 問題是display（）函數。 如何只讀取一行並將其打印在屏幕上？ 提前致謝。

#include <stdio.h>
#include <stdlib.h>     // "stdlib" library contains of exit() and malloc function                        
#include <Windows.h>   // "Windows" library contains of Sleep() function
#include <string.h>   // "string" library contains of strcmp() function

struct personKnowledge
{
    char number[16];
    char name[16];
    char surname[16];
};

void newRecord();
void display();
void deletE();
void add();
void update();

FILE *ptrFILE;

int main()
{
    int choice;
    printf("\n\t\t *-* Phone Book Program *-*");
    do
    {
        printf("\n\n\t\t 1) New record");   // The options are being presented to user
        printf("\n\n\t\t 2) Display person knowledge");
        printf("\n\n\t\t 3) Delete someone");
        printf("\n\n\t\t 4) Add new person");
        printf("\n\n\t\t 5) Update person knowledge");
        printf("\n\n\t\t 6) Exit");
        printf("\n\n\nEnter your choice: ");
        scanf("%d", &choice);
        switch (choice)
        {
        case 1:
        {
            newRecord();
            break;
        }
        case 2:
        {
            display();
            break;
        }
        case 3:
        {
            break;
        }
        case 4:
        {   
            break;
        }
        case 5:
        {
            break;
        }
        case 6:
        {
            printf("\nWorking has been completed.\n");
            exit(0);
            break;
        }
        default:
        {
            printf("\nWrong entry! The program has been terminated.\n");
        }
        }   
    } while (choice >=1 && choice <=6 );
    return 0;
}

void newRecord()
{
    system("cls");   // Screen is being cleaned
    if ((ptrFILE = fopen("Phone Book.txt", "w")) == NULL)
    {
        printf("The file couldn't open\n");
    }
    else
    {          
        struct personKnowledge *p;   // p means person
        p = (struct personKnowledge *)malloc(sizeof(struct personKnowledge));   // Memory is being allocated
        fflush(stdin);
        printf("\n\nDetermine person name: ");   // User is entering the person's knowledge and they are being saved in file
        gets(p->name);
        printf("Determine %s's surname: ", p->name);
        gets(p->surname);
        printf("Determine %s's number: ", p->name);
        gets(p->number);
        fprintf(ptrFILE, "Name\t\t\t\tSurname\t\t\t\t\tNumber\n");
        fprintf(ptrFILE, "--------\t\t   ----------------\t\t\t---------------------\n");
        fprintf(ptrFILE, "\n%s%33s%38s\n", p->name, p->surname, p->number);
        fclose(ptrFILE);
        free(p);
        printf("Please wait, information is saving to file..\n");
        Sleep(1000);
        printf("*-* Saving operation has been completed. *-*");
    }
    fclose(ptrFILE);
}

void display()
{
    struct personKnowledge *s;   // s means searching
    char name[16];
    if ((ptrFILE = fopen("Phone Book.txt", "r")) == NULL)
    {
        printf("The file couldn't open\n");
    }
    else
    {
        fseek(ptrFILE, 0L, SEEK_SET);
        printf("Express name which you search: ");
        gets(s->name);
        while (!feof == NULL)
        {
            fscanf(ptrFILE,"%s", &name);
            if (strcmp(s->name, name) == 0)
            {
                printf("qawsdsdf");
            }
        }
    }
    fclose(ptrFILE);
}

Answer 1

為了回答您的問題之一，建議您在display()重寫此循環

while (!feof == NULL)                   // wrong way to use feof
{
    fscanf(ptrFILE,"%s", &name);        // might overflow the string space
    if (s->name == name)                // wrong way to compare strings
    {
        printf("qawsdsdf");             // missing newline?
    }
}

有了這個

while (fgets(name, sizeof(name), ptrFILE) != NULL)  // safer way to read to a small buffer
{
    name [ strcspn(name, "\r\n") ] = 0; // remove trailing newline etc
    if (strcmp(s->name, name) == 0)     // compare the strings
    {
        printf("qawsdsdf\n");           // added newline
    }
}

編輯在您發布的代碼，甚至不正確編譯任何情況下：

while (!feof == NULL)

是垃圾，應該是

while (!feof(ptrFILE))

盡管正如我所說，反正不是使用feof的方法 。 如果啟用了編譯器警告並對其進行處理，則不會發生這種情況。

Answer 2

我的解決方案是更改文件的格式

fprintf(ptrFILE, "\n%s%33s%38s", p->name, p->surname, p->number);

因為如果您使用程序來檢索信息，則無需在每次寫入信息時都用一堆垃圾標題填充它。 然后，我編輯了顯示功能，以便能夠檢索所述信息。

void display()
{
    struct personKnowledge s;   // s means searching
    char name[16];
    char sname[16];
    char number[16];
    char surname[16];
    if ((ptrFILE = fopen("Phone Book.txt", "r")) == NULL)
    {
        printf("The file couldn't open\n");
    }
    else
    {
        printf("Express name which you search: ");
        scanf("%s", &sname);
        do
        {
            fscanf(ptrFILE,"%s%33s%38s", &name, &surname, &number);
            if (strcmp(sname, name) == 0)
            {
                printf("%s %s %s", name, surname, number);
            }
        }
        while (strcmp(sname, name) != 0);
    }
}

PS我對自己還是個新手，我想我不能為您解釋為什么我的代碼有效而您的代碼無效。 但是我可以說，當我對代碼進行故障排除時，您每次寫入文件的那些標頭都是問題的主要部分。

Answer 3

我認為這些小的更改將解決您的問題

• 分配用於存儲personKnowledge s = (struct personKnowledge *)malloc(sizeof(struct personKnowledge));內存s = (struct personKnowledge *)malloc(sizeof(struct personKnowledge));
• 使文件指針到達數據的起始位置。 已使用一個簡單的技巧來實現此fscanf(ptrFILE, "Name\\t\\t\\t\\tSurname\\t\\t\\t\\t\\tNumber\\n"); fscanf(ptrFILE, "--------\\t\\t ----------------\\t\\t\\t---------------------\\n"); fscanf(ptrFILE, "Name\\t\\t\\t\\tSurname\\t\\t\\t\\t\\tNumber\\n"); fscanf(ptrFILE, "--------\\t\\t ----------------\\t\\t\\t---------------------\\n");
• 在while循環中進行更改。 while (!feof(ptrFILE))
• 掃描一行數據。 fscanf(ptrFILE, "\\n%s%33s%38s\\n", s->name, s->surname, s->number)
• 更改字符串比較。 if (strcmp(name,s->name) == 0)

修改后的顯示功能

    void display(){
      struct personKnowledge *s;   
      s = (struct personKnowledge *)malloc(sizeof(struct personKnowledge));   // Memory is being allocated for s
      fflush(stdin);

      char name[16];
      if ((ptrFILE = fopen("Phone Book.txt", "r")) == NULL)
      {
      printf("The file couldn't open\n");
      }
      else
      {
      fseek(ptrFILE, 0L, SEEK_SET);
      printf("Express name which you search: ");
      scanf("%s",name);     //the name you want to retrieve

      fscanf(ptrFILE, "Name\t\t\t\tSurname\t\t\t\t\tNumber\n");
      fscanf(ptrFILE, "--------\t\t   ----------------\t\t\t---------------------\n");   //when we read the file for first time we need to start from the first location of person data, this is a trick to make ptrFILE reach there
      fflush(stdin);

      while (!feof(ptrFILE))
      {
      fscanf(ptrFILE, "\n%s%33s%38s\n", s->name, s->surname, s->number);//same format as fprintf used in newRecord
        if (strcmp(name,s->name) == 0)   //comparison
        {
            printf("qawsdsdf");
        }
      }}fclose(ptrFILE);}