Thread: Problem reading from external file

Hey im totally new to the boards and c programming and ive been trying to make a program in which the user inputs a username and password

now when they try to login again im having trouble getting the program to read the username(external filename) and the password which is contained inside it.

here is my code...its all messed up cuz i was trying different things. If someone could please tell me how to get it so that it reads the external file("username") and opens it and compares the password inputted by the user and the password contained inside the external file("username") that would be great. Thanks

Code:

void existing()
{
int openFiles('r');
int readDataFromFile();
    //Opens the file from the directory and reads the password
    openFiles('r');
    {
        username = fopen("%s", username, "r");
    } 
    readDataFromFile();
    {
         fgets("%s", username);
    }
        
        extern char username;
    char *fp;
    
    //If statement that confirms the correct username and password
    if (strcmp(user, username) == 0 && strcmp(pass, password) ==0)
    printf("\nAccess Granted\nYou may enter the Matrix\n");
    else
    printf("\n%s is incorrect\nProgram will now terminate.\n\n",password);
         
}

You're also using the wrong syntax for fgets and fopen. I don't see any declaration for password and pass. Also, what is the point of the declaration char *fp, if you're not going to use it.

What are your openFiles and readDataFromFile functions doing?

See your man pages for the proper way to fgets and fopen.

Its horrible to read cuz half of that stuff was me just trying different things
username and password are my only variables.
username is what is inputted by the user and the username is stored as the external filename. Now the password is written to that file. I have all that accomplished but im having a hard time getting it to open the username and match the password inputted by the user and the one that is contained in the file. How do i go about opening the username file and is my if statement enough to compare whats inputted and whats in the file?

Code:

void existing()
{
       username = fopen("%s", username, "r");
       fgets("%s", username);
   
    
    //If statement that confirms the correct username and password
    if (strcmp(user, username) == 0 && strcmp(pass, password) ==0)
    printf("\nAccess Granted\nYou may enter the Matrix\n");
    else
    printf("\n%s is incorrect\nProgram will now terminate.\n\n",password);
         
}

Code:

/* proper use for fopen */
FILE *fp; /* file descriptor */
if((fp = fopen("passwordfile.txt", "r")) == NULL) /* open for path for reading, check for errors */
	perror("passwordfile.txt"), exit(1); /* if error, print the error received and exit*/
		
/* proper use for fgets */
char username[20]; /* declare username as an array of 20 characters */
fgets(username, 20, stdin); /* recieve input from the stdin stream */
username[strlen(username) - 1] = '\0'; /* cut off the '\n' that fgets receives */

k well ive tried that before..and im trying it again all im getting is an error. I just dont get what to put and where and why most importantly
im trying this...

Code:

void existing()
{
    //Opens the file from the directory and reads the password
    FILE *fp;
    if((fp = fopen("&s" ,username, "r")) == NULL)
	perror("%s" ,username);
    
    //If statement that confirms the correct username and password
    if (strcmp(user, username) == 0 && strcmp(pass, password) ==0)
    printf("\nAccess Granted\nYou may enter the Matrix\n");
    else
    printf("\n%s is incorrect\nProgram will now terminate.\n\n",password);
         
}

what i see is that fp=fopen opens the file "username" with the "r" command....i dont see where its reading the file? and i dont see why this doesnt work

Code:

if((fp = fopen("&s" ,username, "r")) == NULL)
	perror("%s" ,username);

fopen() only opens the file for reading, it doesn't do any reading itself. The arguments for fopen "&s", username will not do anything but give an error. The syntax for fopen is:
FILE *fopen(const char * restrict path, const char * restrict mode);
fp = fopen("file.txt", "r"); will open file.txt for reading.

perror is not like printf, it's syntax is:
void perror(const char *string);
perror(""); will print the error without any text before it. perror("file.txt") will print file.txt: [error here]. perror() does NOT accept arguments like printf and such does.

There are many ways to read from a file once you have open, I suggest you search the forums or google for how to do that. If you have problems, post your problem and code.

fp = fopen("file.txt", "r"); will open file.txt for reading.

well for this i see that is does that
but as there is user input i cannot put in file.txt its a variable thats why i use %s.

k so far you guys have been of no help

please help i need this finished by tonight

ALSO
how do i clear the screen after a function has completed?
what library is needed and whats the command?

FAQ > How do I... (Level 1) > Get a line of text from the user/keyboard (C)

that was of no use to me
however i did get the clrscr to work thank you

Originally Posted by coolshyam

Code:

int main()
{
	FILE *fp;
	char shyam[10],usr[10];
	fp=fopen("c:\\winnt\\temp\\user.txt","r");
	fgets(usr,10,fp);
        if(usr[strlen(usr) - 1] == '\n')
                 usr[strlen(usr) - 1] = '\0';
	scanf("%s",shyam);
	if(strcmp(shyam,usr)==0)
	{
		printf("correct")
	}
	return 0;
}

You forgot to remove the '\n' from fgets(). Some people will also say scanf() is bad to use, so I suggest to use fgets() again.