C:gets()跳过第一个输入 [英] C: gets() skips the first input

问题描述

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>


typedef struct record
{   
    char name[20];
    char surname[20];
    char telephone[20];

}Record;

typedef struct node
{
    Record data;
    struct node *next;
}Node;

Node *head = NULL;

void addRecord(Record s)
{
    Node *newNode;
    Node *n;

    newNode = (Node*)malloc(sizeof(Node));
    newNode->data = s;
    newNode->next = NULL;

    if (head == NULL)
    {
        // The linked list is empty
        head = newNode;
    }
    else
    {
        // Traverse the whole list until we arrive at the last node
        n = head;
        while (n->next != NULL)
        {
            n = n->next;
    }
        n->next = newNode;
    }
}

Record enterRecordDetails()
{
    Record aRecord;
    int len;
    int valid = 0;
    int valid2 = 0;
    printf("ENTER THE FOLLOWING RECORD DETAILS:\n");

    printf("   NAME      : ");
    gets(aRecord.name);
    printf("   SURNAME   : ");
    gets(aRecord.surname);  
    do {
        valid = 0;
        valid2 = 0;
        printf("  TELEPHONE NO. (8 digits): ");
        gets(aRecord.telephone);
        len = strlen(aRecord.telephone);
        for (int i = 0; i < len; i++)
        {
            if (!isdigit(aRecord.telephone[i])) {
                printf("You enterred an invalid number\n");
                valid = 1; break;
            }
        }
        Node *p = head;         
            while (p != NULL)
            {
                Node *next = p->next;
                for (; next; p = next, next = next->next) {
                    if (strcmp(p->data.telephone, aRecord.telephone) == 0)
                    {
                        valid2 = 1; break;
                    }
                }
                if(p = NULL)break;
            }

    } while((valid == 1) || (len != 8) || (valid2 == 1));
    getchar();
    fflush(stdin);
    return aRecord;
}


int main(void)
{
    char menuOption;

    do
    {
        system("cls");
        printf("~~~ MAIN MENU ~~~\n");
        printf("1. Add Telephone Record\n");
        printf("2. Delete Telephone Record\n");
        printf("3. Search\n");
        printf("4. Display All Records\n");
        printf("5. Exit\n\n");
        menuOption = getchar();
        fflush(stdin);
        switch (menuOption)
     {
    case '1':
        addRecordToList();
        break;
    case '4':
        displayList();
        break;
    }

} while (menuOption != '5');

getchar();
return 0;

}

添加学生时，计算机会要求用户输入姓氏而不是姓名.为什么程序跳过名称"?显示名称"，但是希望用户改写姓氏.

When adding a student, the computer asks the user to enter the surname rather than the name. Why is the program skipping 'Name' ? 'Name' is displayed, however the user is expected to write the surname instead.

推荐答案

首先，不要使用gets，这是不安全的.代替使用 fgets .

First, do not use gets, it's unsafe. Use fgets instead.

第一次调用gets跳过行的原因是，在调用enterRecordDetails()时缓冲区中有一个'\n'.通常，'\n'是早期输入操作(例如，用scanf读取int)的遗留物.

The reason why the first call to gets skips a line is that there is a '\n' in the buffer at the time that you are making a call to enterRecordDetails(). Typically, the '\n' is a leftover from an earlier input operation, for example, from reading an int with scanf.

解决此问题的一种方法是在读取int时将字符串读取到末尾，以便连续调用fgets将获得实际数据.您可以在enterRecordDetails()函数中完成此操作:

One way to fix this problem is to read the string to the end when reading the int, so that the consecutive call of fgets would get the actual data. You can do it in your enterRecordDetails() function:

Record enterRecordDetails()
{
    Record aRecord;
    printf("ENTER THE FOLLOWING RECORD DETAILS:\n");
    printf("   NAME      : ");
    fscanf(stdin, " "); // Skip whitespace, if any
    fgets(aRecord.name, 20, stdin);
    printf("   SURNAME   : ");
    fgets(aRecord.surname, 20, stdin);  
}

但是，请注意，fgets将'\n'保留在字符串中，只要它适合缓冲区即可.更好的方法是使用scanf，并传递一个格式说明符，该说明符限制输入的长度并在'\n'处停止:

Note, however, that fgets keeps '\n' in the string, as long as it fits in the buffer. A better approach would be using scanf, and passing a format specifier that limits the length of input and stops at '\n':

scanf(" %19[^\n]", aRecord.name);
//     ^

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