segmentation fault using scanf [duplicate] - c

Question

This question already has answers here:
using scanf function with pointers to character
(6 answers)
Closed 3 years ago.
noob question here:
I'm trying to write a simple menu interface, but I keep getting a segmentation fault error and I can't figure out why.
#include <stdlib.h>
#include <stdio.h>
int flush(); int add(char *name, char *password, char *type); int delete(char *name);
int edit(char *name, char *password, char *type, char *newName, char *newPassword, char *newType);
int verify(char *name, char *password);
int menu(){
int input;
char *name, *password, *type, *newName, *newPassword, *newType;
printf("MAIN MENU \n ============\n");
printf("1. ADD\n");
printf("2. DELETE\n");
printf("3. EDIT\n");
printf("4. VERIFY\n");
printf("5. Exit\n");
printf("Selection:");
scanf("%d", &input);
flush();
switch (input){
case 1:
printf("%s\n", "Enter Name:");
scanf("%s", name);
flush();
printf("%s\n", "enter password" );
scanf("%s", password);
flush();
printf("%s\n","enter type" );
scanf("%s",type);
add(name, password, type);
menu();
break;
case 2:
printf("Enter Name:" );
scanf("%s",name);
flush();
delete(name);
menu();
break;
case 3:
printf("Enter Name:\n");
scanf("%s",name);
flush();
printf("Enter Password\n");
scanf("%s", password);
flush();
printf("enter type:\n");
scanf("%s", type);
flush();
printf("enter your new username:\n");
scanf("%s",newName);
flush();
printf("enter your new password\n");
scanf("%s", newPassword);
flush();
printf("enter your new type\n");
scanf("%s",newType);
flush();
edit(name, password, type, newName, newPassword, newType);
menu();
break;
case 4:
printf("Enter Name\n");
scanf("%s",name);
flush();
printf("Enter Password\n");
scanf("%s",password);
flush();
verify(name, password);
menu();
break;
case 5:
return 0;
default:
printf("invalid input, please select from the following:\n");
menu();
}
return 0;
}
int flush(){
int ch;
while ((ch = getchar()) != EOF && ch != '\n') ;
return 0;
}
I get the segmentation fault after entering two fields, in any menu option

Answer 1

You need to initialize your pointers. Alternatively, use stack-allocated arrays.
For example, instead of char *name, do char name[20]. (Note that this will limit your input to 19 characters; use a larger buffer if necessary.)
Right now, you are passing uninitialized pointers into scanf() which effectively means that scanf() is going to write to an undefined area of memory. It might work on one execution and then fail on the next. It might corrupt memory elsewhere in the process' address space.
Don't use uninitialized variables, and consider turning up your compiler warnings as high as they will go; the compiler can catch errors like this and emit a warning.

Answer 2

Instead of using *name, *password,.. use name[100], password[100],... If you want name, password, .. to be pointer then allocate memory using malloc or calloc before calling scanf.