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我有一个项目中的这2个函数加载并保存用户的信息到一个文件中。每个用户都保存在文件的新行中。我的问题是,当我尝试使用ftell(f)时,程序崩溃。当我打印ftell(f)后,它用fopen()打开文件后打印-1。我尝试在errno中看到错误,但是它在fopen()后打印出“NO ERROR”,但当我使用fseek修改文件指针f位置时,会显示“INVALID ARGUMENT”。为什么ftell打印-1作为文件指针的值?为什么errno打印出“INVALID ARGUMENT”?
我的问题是在我的Load_File函数,但我也显示了Save_File函数也检查我在文件中正确写入。
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
LIST Load_File(LIST L){
//PRE: receive a void list (L==NULL)
//POST: returns an user's loaded from file
USER user; //node of list
char str[150];
//User's structure
char name[30];
char CI[10];
char email[30];
char city[30];
char password[30];
errno=0;
FILE *f;
if(f=fopen("DATOS.txt","r")==NULL){
printf("File not found. \n");
return L;
}
//Code for verify what's happening
printf("FTELL: %d/n", ftell(f)); //prints -1
printf("ERRNO: %s\n", strerror(errno)); //prints NO ERROR
fseek(f, 0, SEEK_CUR);
printf("FTELL: %d\n", ftell(f)); //still prints -1
printf("ERRNO: %s\n", strerror(errno)); //prints INVALID ARGUMENT
printf("FEOF: %d\n",feof(f)); //CRASHES! (a)
while(feof(f)==0){ //CRASHES when (a) line is deleted
//Load line of file in user's structure
fgets(str, 150, f);
sscanf(str,"%s %s %s %s %s ",name, CI, email, city, password);
//Copy into structure's parts
strcpy(user->name, name);
strcpy(user->CI, CI);
strcpy(user->email, email);
strcpy(user->city, city);
strcpy(user->password, password);
Add_user_to_list(L, user);
}
if(fclose(f)!=0) printf("\n\n FILE NOT PROPERLY ClOSED \n\n");
}
void Save_File(LIST L){
//PRE: receive an user's list
//POST: saves a new list in file
FILE *f;
int flag=0;
f=fopen("DATOS.txt","w");
if(f==NULL){
printf("Error opening file f\n");
}
if(!L_Void(L)){
L=L_First(L);
do{
if(flag) L=L_Next(L);
flag=1;
fprintf(f,"%s %s %s %s %s \n",L_InfoM(L)->name,L_InfoM(L)->CI, L_InfoM(L)->email, L_InfoM(L)->city, L_InfoM(L)->password);
}while(!L_Final(L));
}else printf("List is void, then nothing was saved.\n");
if(fclose(f)!=0) printf("\n\n FILE NOT PROPERLY COSED \n\n");
}
'(NULL == f)'是不必要的;你可以简单地写'(f)',因为它基本上会自动与0进行比较。 –
谢谢!我曾尝试过两行,但我当然误解了时间的结果。至少这让我强化了优先重要性! –
@MDXF“'(NULL == f)'是不必要的;你可以简单地写'(f)'''(NULL == f)'相当于'(!f)'。现在你明白了为什么我倾向于实现与NULL的比较。 –