fgets - crashes in visual studio, works in gcc - c

Question

I'm working on something small and I have run into a really small but disturbing problem - the program works in gcc, but crashes in visual studio, when it gets to the fgets command:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
void registerUser(char *username);
char path[256] = "C:\\Users\\magshimim\\Desktop\\cproject\\bank\\";
int main() {
int choice = 0;
char username[10];
printf("Welcome to nikitosik's bank program!\n"
"Choose an option :\n"
"0 - Register\n"
"1 - Login to existing account\n");
scanf("%d", &choice);
getchar(); // catch enter
if (!choice) {
registerUser(username);
} else {
//login();
}
}
void registerUser(char *username) { // username is passed, for verification later
FILE *userinfo; // file that contains info of all registered users
FILE *userpathf; // file to open for txt file
char usertxt[256]; // path of data
char userpath[256]; // path of new user data file
char password[15];
strcat(userpath, path);
strcat(usertxt, path);
strcat(usertxt, "users.txt");
userinfo = fopen(usertxt, "a");
printf("Choose a username(max 10 letters): ");
fgets(username, 10, stdin);
username[strcspn(username, "\n")] = 0;
strcat(userpath, username);
strcat(userpath, ".txt");
userpathf = fopen(userpath, "w");
fclose(userpathf);
printf("Choose a password(max 15 letters): ");
fgets(password, 15, stdin);
fprintf(userinfo, "%s\n%s", username, password);
fclose(userinfo);
}
thanks in advance

Answer 1

As above really or initialize the strings first.
memset(userpath, 0, sizeof(userpath));
memset(usertxt, 0, sizeof(usertxt));

Answer 2

Your program has multiple issues:
you concatenate a string into an uninitialized array: this has undefined behavior and may well explain the observed behavior on different systems as undefined behavior may take multiple forms from no consequence at all to a crash or possibly even worse misfortune.
you do not test the return values of scanf, fopen, fgets(). Any invalid or unexpected input may trigger more undefined behavior.
you do not check for potential buffer overflow in strcat(). You should instead use snprintf().
Here is a safer version:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int registerUser(char *username, size_t size);
char path[] = "C:\\Users\\magshimim\\Desktop\\cproject\\bank\\";
int main(void) {
int choice = 0;
int c;
char username[10];
printf("Welcome to nikitosik's bank program!\n"
"Choose an option :\n"
"0 - Register\n"
"1 - Login to existing account\n");
if (scanf("%d", &choice) != 1)
return 1;
// consume the rest if the input line
while ((c = getchar()) != EOF && c != '\n')
continue;
if (choice == 0) {
registerUser(username, sizeof(username));
} else {
//login();
}
return 0;
}
int registerUser(char *username, size_t size) { // username is passed, for verification later
char usertxt[256]; // path of data
char userpath[256]; // path of new user data file
char password[17];
FILE *userinfo; // file that contains info of all registered users
FILE *userpathf; // file to open for txt file
printf("Choose a username(max %d letters): ", (int)(size - 2));
if (!fgets(username, size, stdin))
return -1;
username[strcspn(username, "\n")] = 0; // strip newline if any
printf("Choose a password(max 15 letters): ");
if (!fgets(password, sizeof(password), stdin))
return -1;
password[strcspn(password, "\n")] = 0; // strip newline if any
if (snprintf(usertxt, sizeof(usertxt), "%s%s", path, "users.txt") >= (int)sizeof(usertxt))
return -1;
if (snprintf(userpath, sizeof(userpath), "%s%s.txt", path, username) >= (int)sizeof(userpath))
return -1;
userinfo = fopen(usertxt, "a");
if (userinfo == NULL)
return -1;
// create user file
userpathf = fopen(userpath, "w");
if (userpathf != NULL)
fclose(userpathf);
// add user info
fprintf(userinfo, "%s\n%s\n", username, password);
fclose(userinfo);
return 0;
}