dynamic 2d char array in c - c++

Question

I want to take username and passwords from client and check that this username already didn't exist, but it doesn't work and this error happens:
Exception thrown at 0x51D20ED2 (ucrtbased.dll) in project3.exe: 0xC0000005:
Access violation reading location 0xCDCDCDCD.>
I don't know why?
This is my code:
void signup(char *input, char **usernames,int *userindex,char **passwords)
{
int check = 0;
char *ptr1,*ptr2;
ptr1 = (char*)malloc(strlen(input)*sizeof(char));
ptr2 = (char*)malloc(strlen(input)*sizeof(char));
strtok(input, " ");
strcpy(ptr1, strtok(NULL," "));
strcpy(ptr2, strtok(NULL," "));
for (int i = 1; i < *(userindex); i++)
{
if (!(strcmp(ptr1,usernames[i])))
{
check = 1;
printf("this user has already signed up\n");
break;
}
}
if (check == 0)
{
usernames[*(userindex)] = (char*)malloc((strlen(ptr1))* sizeof(char));
passwords[*(userindex)] = (char*)malloc((strlen(ptr2))* sizeof(char));
strcpy(usernames[*(userindex)], ptr1);
strcpy(passwords[*(userindex)], ptr2);
printf("%s\n%s\n%d\n", usernames[*(userindex)], passwords[*(userindex)], *(userindex));
*(userindex) = *(userindex)+1;
free(ptr1);
free(ptr2);
}
}
int main()
{
int quit = 0;
char *input, **usernames, **passwords;
int state, length, userindex = 1;
usernames = (char**)malloc(sizeof(char*));
passwords = (char**)malloc(sizeof(char*));
while (quit == 0)
{
int counter = 1;
char buffer;
input = (char*)malloc(sizeof(char));
printf("please enter your action\n");
do
{
buffer = getchar();
input = (char*)realloc(input, counter*sizeof(char));
input[counter - 1] = buffer;
counter++;
} while (buffer != '\n');
input = (char*)realloc(input, (counter)*sizeof(char));
input[counter - 1] = '\0';
state = action_decider(input);
switch (state)
{
case 0:
break;
case 1:
break;
case 2:
break;
case 3:
break;
case 4:
usernames = (char**)realloc(usernames,userindex*sizeof(char*));
passwords = (char**)realloc(passwords,userindex*sizeof(char*));
signup(input, usernames, &(userindex), passwords);
break;
case 5:
break;
case 6:
quit = 1;
break;
case 7:
printf("you command nonsence!\n");
break;
}
}
return 0;
}