c - c中模块中 undefined symbol _system

Question

我有这个代码。我收到链接器错误。我不知道这个链接器错误是什么。请帮我。我正在使用 Turbo C++ 编译器来编写此代码。

#include<string.h>
#include<process.h>
#include<stdlib.h>
#include<dos.h>
struct contact
{
  long ph;
 char name[20],add[20],email[30];

};
struct contact list;
char query[20],name[20];
FILE *fp, *ft;
int i,n,ch,l,found;

void main()
{
start:
system("cls");    /* ************Main menu ***********************  */
printf("\n\t **** Welcome to a0 contact Manager ****");
printf("\n\n\n\t\t\tMAIN MENU\n\t\t=====================\n\t\t[1] Add    a new Contact\n\t\t[2] List all Contacts\n\t\t[3] Search for contact\n  \t\t[4] Edit a Contact\n\t\t[5] Delete a Contact\n\t\t[0] Exit\n\t\t=================\n\t\t");
printf("Enter the choice:");
scanf("%d",&ch);
switch(ch)
{
    case 0:
    printf("\n\n\t\tAre you sure u want to exit?");
    break;
    /* *********************add new contacts************  */

    case 1:
    system("cls");
    fp=fopen("contact.dll","a");
    for(;;)
    {
        fflush(stdin);
        printf("To exit enter blank space in the name input\nName (Use identical):");
        scanf("%[^\n]",&list.name);
        if(stricmp(list.name,"")==0 || stricmp(list.name," ")==0)
        break;
        fflush(stdin);
        printf("Phone:");
        scanf("%ld",&list.ph);
        fflush(stdin);
        printf("address:");
        scanf("%[^\n]",&list.add);
        fflush(stdin);
        printf("email address:");
        gets(list.email);
        printf("\n");
        fwrite(&list,sizeof(list),1,fp);
    }
    fclose(fp);
    break;

    /* *********************list of contacts*************************  */

    case 2:
    system("cls");
    printf("\n\t\t================================\n\t\t\tLIST OF CONTACTS\n\t\t================================\n\nName\t\tPhone No\t    Address\t\tE-mail ad.\n=================================================================\n\n");
    for(i=97;i<=122;i=i+1)
    {
        fp=fopen("contact.dll","r");
        fflush(stdin);
        found=0;
        while(fread(&list,sizeof(list),1,fp)==1)
        {
            if(list.name[0]==i || list.name[0]==i-32)
            {
                printf("\nName\t: %s\nPhone\t: %ld\nAddress\t: %s\nEmail\t: %s\n",list.name,list.ph,list.add,list.email);
                found++;
            }
        }
        if(found!=0)
        {
            printf("=========================================================== [%c]-(%d)\n\n",i-32,found);
            getch();
        }
        fclose(fp);
    }
    break;

    /* *******************search contacts**********************  */
    case 3:
    system("cls");
    do
    {
        found=0;
        printf("\n\n\t..::CONTACT SEARCH\n\t===========================\n\t..::Name ofcontact to search: ");
        fflush(stdin);
        scanf("%[^\n]",&query);
        l=strlen(query);
        fp=fopen("contact.dll","r");
        system("cls");
        printf("\n\n..::Search result for '%s' \n===================================================\n",query);
        while(fread(&list,sizeof(list),1,fp)==1)
        {
            for(i=0;i<=l;i++)
            name[i]=list.name[i];
            name[l]='\0';
            if(stricmp(name,query)==0)
            {
                printf("\n..::Name\t: %s\n..::Phone\t: %ld\n..::Address\t: %s\n..::Email\t:%s\n",list.name,list.ph,list.add,list.email);
                found++;
                if(found%4==0)
                {
                    printf("..::Press any key to continue...");
                    getch();
                }
            }
        }
        if(found==0)
            printf("\n..::No match found!");
        else
            printf("\n..::%d match(s) found!",found);
        fclose(fp);
        printf("\n ..::Try again?\n\n\t[1] Yes\t\t[0] No\n\t");
        scanf("%d",&ch);
    }
    while(ch==1);
    break;


    /* *********************edit contacts************************/
    case 4:
    system("cls");
    fp=fopen("contact.dll","r");
    ft=fopen("temp.dat","w");
    fflush(stdin);
    printf("..::Edit contact\n===============================\n\n\t..::Enter the name of contact to edit:");
    scanf("%[^\n]",name);
    while(fread(&list,sizeof(list),1,fp)==1)
    {
        if(stricmp(name,list.name)!=0)
        fwrite(&list,sizeof(list),1,ft);
    }
    fflush(stdin);
    printf("\n\n..::Editing '%s'\n\n",name);
    printf("..::Name(Use identical):");
    scanf("%[^\n]",&list.name);
    fflush(stdin);
    printf("..::Phone:");
    scanf("%ld",&list.ph);
    fflush(stdin);
    printf("..::address:");
    scanf("%[^\n]",&list.add);
    fflush(stdin);
    printf("..::email address:");
    gets(list.email);
    printf("\n");
    fwrite(&list,sizeof(list),1,ft);
    fclose(fp);
    fclose(ft);
    remove("contact.dll");
    rename("temp.dat","contact.dll");
    break;

    /* ********************delete contacts**********************/
    case 5:
    system("cls");
    fflush(stdin);
    printf("\n\n\t..::DELETE A CONTACT\n\t==========================\n\t..::Enter the name of contact to delete:");
    scanf("%[^\n]",&name);
    fp=fopen("contact.dll","r");
    ft=fopen("temp.dat","w");
    while(fread(&list,sizeof(list),1,fp)!=0)
    if (stricmp(name,list.name)!=0)
        fwrite(&list,sizeof(list),1,ft);
    fclose(fp);
    fclose(ft);
    remove("contact.dll");
    rename("temp.dat","contact.dll");
    break;

    default:
    printf("Invalid choice");
    break;
}
printf("\n\n\n..::Enter the Choice:\n\n\t[1] Main Menu\t\t[0] Exit\n");
scanf("%d",&ch);
switch(ch)
{
    case 1:
    goto start;
    case 0:
    break;
    default:
    printf("Invalid choice");
    break;
}
}

我遇到了这个错误。c 中模块中 undefined symbol _system。

Answer 1

undefined symbol _system链接器错误意味着链接器找不到任何(静态)库代码来链接您的system("cls")调用。对于 Turbo C++，这可能意味着您必须在项目配置中指定额外的库。

如果您使用现代 C 编译器，例如 GCC 或 Clang(许多系统都可以免费使用)，则不会遇到此问题。