C语言中的读/写功能

Question

典型的初学者电话簿程序，尝试添加对文件的读写功能。 它没有编译是因为

1）无论我将其放置在哪里，它都不会识别标签ErrorHandler

2）在两个函数中：从不兼容的指针类型传递fprintf参数2 [默认启用]

3）在.c文件随附的文件中，在两个函数中均进行了打印：预期的const char * __restrict__但参数的类型为struct pb *

整个代码：

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

typedef struct phonebook {
   char cFirstName[20];
   char cLastName[20]; 
   char PhoNo[20]; 
} pb; 

//function prototypes
void AddContact (pb * ); 
void DeleteContact (pb * ); 
void ShowContacts (pb * ); 
void FindContact (pb * );
void RandContact (pb * );
void FindContact (pb * );
void DeleteAll (pb *);
void Read  (pb *);
void Write (pb *);

char FileName[100]; 
FILE *pRead; 
FILE *pWrite; 

int counter = 0;

main ()
{
    pb *phonebook; 
    phonebook = (pb*) malloc(sizeof(pb)*1);
    int iChoice = 0;

    while (iChoice <= 8) {
        printf("\n-Choose an option- \n");
        printf("\n\t(1)\tAdd Contact");
        printf("\n\t(2)\tDelete Contact");
        printf("\n\t(3)\tShow All Contacts");
        printf("\n\t(4)\tSearch for a Contact");
        printf("\n\t(5)\tRandom Contact");
        printf("\n\t(6)\tDelete All Contacts");
        printf("\n\n\t(7)\tWrite contacts to file");
        printf("\n\t(8)\tRead contacts from file");
        printf("\n\n\t(9)\tExit\n\n\t");

        scanf("%d", &iChoice); 

        if (iChoice == 1) {
            AddContact(phonebook); 
        } 

        if (iChoice == 2) {
            DeleteContact (phonebook); 
        } 

        if (iChoice == 3) {
            ShowContacts(phonebook); 
        } 

        if (iChoice == 4) {
            FindContact(phonebook); 
        }

        if (iChoice == 5) {
            RandContact(phonebook);
        }

        if (iChoice == 6) { 
            DeleteAll(phonebook);
        }

        if (iChoice == 7) {
            Write(phonebook);
        }

        if (iChoice == 8) {
            Read(phonebook);
        }  

        if (iChoice == 9) {
            free(phonebook);
            return 0;
        }           
    } //end while
} //end main

//function definitions

//add contact
void AddContact (pb * phonebook)
{  
    counter++; //counter incremented for each entry
    realloc(phonebook, sizeof(pb)); //realloc with every new contact
    printf("\nFirst Name: ");
    scanf("%s", phonebook[counter-1].cFirstName);
    printf("Last Name: ");
    scanf("%s", phonebook[counter-1].cLastName);
    printf("Phone Number: ");
    scanf("%s", phonebook[counter-1].PhoNo);
    printf("\n\tContact added\n"); 
}

//delete contact
void DeleteContact (pb * phonebook)
{
    int x = 0;
    char scrapcFirstName[20];  //strings for deleting original strings
    char scrapcLastName[20];  
    char nullStr[20] = {"\0"}; 

    printf("\nFirst name: ");
    scanf("%s", scrapcFirstName);
    printf("Last name: ");
    scanf("%s", scrapcLastName);
    //compare strings
    for (x = 0; x < counter; x++) {
        if (strcmp(scrapcFirstName, phonebook[x].cFirstName) == 0) {
            for (x = 0; x < counter; x++) {
                if (strcmp(scrapcLastName, phonebook[x].cLastName) == 0) {
                    strcpy(phonebook[x].cFirstName, nullStr); 
                    strcpy(phonebook[x].cLastName, nullStr); 
                    strcpy(phonebook[x].PhoNo, nullStr);
                }//end if
                else {
                    printf("Invalid Input");
                }
            }//end for
        }//end if
    }// end for

    counter--;   // Contact deleted, update counter
    printf("Contact Deleted\n");
} 

//show phonebook
void ShowContacts (pb * phonebook)
{
    int x = 0;
    printf("\nPhonebook:\n\n ");
    for( x = 0; x < counter; x++) {
        printf("\n(%d)\n", x+1);
        printf("Name: %s %s\n", phonebook[x].cFirstName, phonebook[x].cLastName);
        printf("Number: %s\n", phonebook[x].PhoNo); 
    } //end for
}

//Find a specific contact
void FindContact (pb * phonebook)
{
    int x = 0;
    char TempFirstName[20]; 
    char TempLastName[20]; 

    printf("\nWho are you looking for?");
    printf("\n\nFirst Name: ");
    scanf("%s", TempFirstName);
    printf("Last Name: ");
    scanf("%s", TempLastName);

    for (x = 0; x < counter; x++) {
        if (strcmp(TempFirstName, phonebook[x].cFirstName) == 0) {
            if (strcmp(TempLastName, phonebook[x].cLastName) == 0) {
                printf("\n%s %s \n%s\n", phonebook[x].cFirstName,
                                         phonebook[x].cLastName,
                                         phonebook[x].PhoNo);
            } 
        } 
    }     
}    

//show a random contact
void RandContact (pb * phonebook)
{
    int iRand = 0;
    srand(time(NULL));
    iRand = rand() % counter;  
    int x = iRand; 

    printf("\n%s %s\n", phonebook[x].cFirstName, phonebook[x].cLastName);
    printf("%s\n", phonebook[x].PhoNo);
}    

//delete all
void DeleteAll (pb * phonebook)
{
    int x = 0;
    char nullStr[20] = {'\0'}; 

    for ( x = 0; x < counter; x++) {
        strcpy(phonebook[x].cFirstName, nullStr); 
        strcpy(phonebook[x].cLastName, nullStr); 
        strcpy(phonebook[x].PhoNo, nullStr); 
        --counter; 
    }   

    printf("Contacts have been wiped.\n");     
} 

void Read(pb * phonebook)
{
    FILE *pRead;
    char name[256];

    printf("File to read:");
    gets(name);
    pWrite=fopen(name,"a");

    if(pWrite != NULL) {
        printf("Contact List");
        while(!feof(pRead)) {
            fprintf(pRead, phonebook,sizeof (struct phonebook));
            if (!feof(pRead)) {
                fprintf(pRead, phonebook,sizeof (struct phonebook));
            }
        }
    }
    else {
        goto ErrorHandler;
    }

    exit(EXIT_SUCCESS);

ErrorHandler:
    perror("The folling error occured:");
    exit(EXIT_FAILURE);
}

void Write(pb * phonebook)
{
    FILE *pWrite;
    char name[256];

    printf("File to write:");
    gets(name);
    pWrite=fopen(name,"a");

    if(pWrite != NULL) {
        fprintf(pWrite, phonebook,sizeof (struct phonebook));
        fclose(pWrite);
    }
    else {
        goto ErrorHandler;
    }

    exit(EXIT_SUCCESS);

ErrorHandler:
    perror("The folling error occured:");
    exit(EXIT_FAILURE);
}

Answer 1

Q1。 根据C标准的6.8.6.1节：

goto语句中的标识符应命名位于封闭函数中某处的标签。

goto语句不应从具有可变修改类型的标识符范围外跳到该标识符范围内。

goto语句会导致无条件跳转到封闭函数中以命名标签为前缀的语句。

教授要讲的是，您需要将每个函数内的goto放到底部的一个部分，该部分处理相对于该函数的清理（关闭文件等），然后执行return 。 良好使用goto （和不好使用）的示例如下 ： C或C ++中良好的goto 示例

Q2。 这意味着printf中的格式说明符与传递的参数类型不匹配。 在这种情况下，您正在执行以下操作：

fprintf(pRead, phonebook, sizeof (struct phonebook));

fprintf将char *作为指定格式的字符串。 您永远都不要直接传递结构（想象一下，如果您使用fprintf且电话簿条目具有%登录符号，将会发生什么情况）。

在这种情况下，您要向文件写入固定大小的对象，而不是以NULL结尾的字符串。 因此，无论如何您都应该使用fwrite而不是fprintf ，例如

fwrite(phonebook, sizeof (struct phonebook), 1, pRead);

您还应该考虑错误检查，以及pRead是否是您正在写入的FILE *的好名字。

Q3。 请参阅第2季。

Answer 2

您应该将电话簿转换为char *：

fprintf(pWrite, (char*)phonebook,sizeof (struct phonebook));

goto不能在不同功能之间跳转。
您需要在每个函数中都有一个“ ErrorHandler”标记。

也许更好的解决方案是万客隆。