String array comparing with user string gives access error - c

Question

I am trying to build a program which will take in a list of login details (usernames and passwords) from a file and allow you the option to enter a username and password which are compared with the approved logins and a result is given. In my strcmp I am receiving access violation error 0xC0000005.
#include <stdio.h>
#include <conio.h>
#include<stdlib.h>
FILE *fptr;
void main();
void openFile();
void closeFile();
char approvedUsrnames[3][6];
char approvedPassword[3][6];
void main()
{
char userPassword[6], usrname[6], inputChar, fileString[6];
int i;
openFile();
int numofLogins= 3;
if (fptr != NULL)
{
printf("\nReading file with scanf\n");
while (!feof(fptr))
{
for (i = 0; i < 3; i++) {
fgets(approvedUsrnames[i], 6, fptr);
fgets(approvedPassword[i], 6, fptr);
}
}
closeFile();
}
printf("Enter User name: ");
scanf("%s",usrname);
printf("Enter the password <any 6 characters>: ");
for (i = 0; i<6; i++)
{
inputChar = _getch();
userPassword[i] = inputChar;
inputChar = '*';
printf("%c", inputChar);
}//obfuscate the input to the user
/*If you want to know what you have entered as password, to be removed*/
printf("\nYour password is %s:", userPassword);
for (i = 1; i < 3; i++) {
printf("\Username is good %s\n", approvedUsrnames[i]);
if (strcmp(approvedUsrnames[i], usrname == 0)){
printf("\Username is good\n");
if (strcmp(userPassword, approvedPassword[i]) == 0) {
printf("\nPassword is good\n");
}//end nested if
else {
printf("\nPassword is not match\n");
}
}//end if
}//end for
_getch();
}
void openFile()
{
fptr = fopen("approvedLogins.dat", "r");
if (fptr == NULL)
{
printf("Error opening file ! \n");
}
else {
printf("Login file read successfully ! \n");
}
}
void closeFile()
{
fclose(fptr);
}

Answer 1

#anthonygordon
It is very likely that the strings usrname and userPassword aren't being terminated with '\0' (null terminator) a) as the scanf() may attempt to fill in more chars than usrname can capture b) for loop has to iterate only 5 times so that userPassword[5] is to be explicitly set to '\0'. (If the expectation is to use 6 character long username and password, then change the length of array from 6 to 7 and make sure array[6] is filled with '\0') (Remember in 'C' array subscripts goes as 0..(arraysize-1))
Also, once the user name and password matches, break-out from the loop.

Answer 2

You picked specific lengths for your username and password character arrays. This means that you know the amount of characters you want to compare.
In such a case you do not need to add a '/0' to your character array. Simply use the strncmp() function and specify the number of characters to compare in the second parameter.
See: http://www.tutorialspoint.com/c_standard_library/c_function_strncmp.htm
Just a tip:
Test after every bit of code that you add. This way it is easy to know what code caused the problem. Only when you get really experienced (perhaps 4+ years of coding) can you be brave and write more code before testing.