C struct field assignment overwrites another field - c

Question

I am writing a fantasy football draft program for fun.
I encountered a strange problem. I assign a value to a struct field and that happens, but it also assigns that value to another field in the struct. Apologies for the messy debugging printf statements.
I clearly don't understand something about struct field assignment.
code:
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#define TRUE 1
int QB_count = 0;
int RB_count = 0;
int WR_count = 0;
int TE_count = 0;
int DEF_count = 0;
struct Player {
char *name;
char *position;
int age;
int bye_week;
};
int get_name (struct Player *drafted) {
char name[20];
fputs("Enter Player Name: ", stdout);
fflush(stdout);
if (fgets(name, sizeof name, stdin) != NULL){
char *newline = strchr(name, '\n');
if (newline != NULL){
*newline = '\0';
}
drafted->name = name;
printf("You've drafted: %s\n", drafted->name);
}
return 0;
}
int get_position(struct Player *drafted){
char position[20];
int depth;
char *nametemp = drafted->name;
printf("nametemp: %s\n", nametemp);
fputs("Enter Player Position in 'QB/RB/WR/TE/DEF' format: ", stdout);
fflush(stdout);
if (fgets(position, sizeof position, stdin) != NULL){
char *newline = strchr(position, '\n');
if (newline != NULL){
*newline = '\0';
}
drafted->position = position;
if (strcmp(position, "QB") == 0){
QB_count++;
depth = QB_count;
} else if (strcmp(position, "RB") == 0){
RB_count++;
depth = RB_count;
} else if (strcmp(position, "WR") == 0){
WR_count++;
depth = WR_count;
} else if (strcmp(position, "TE") == 0){
TE_count++;
depth = TE_count;
} else if (strcmp(position, "DEF") == 0){
DEF_count++;
depth = DEF_count;
} else {
printf("Please re-enter position information using the format 'QB' or 'qb'\n");
get_position(drafted);
return 0;
}
drafted->name = nametemp;
printf("NAME: %s\n", drafted->name);
printf("You've drafted %s at: %s%d\n", drafted->name, drafted->position, depth);
}
return 0;
}
int get_age (struct Player *drafted){
return 0;
}
int get_bye_week (struct Player *drafted){
return 0;
}
int main (){
int stop = 0;
char text[20];
while (TRUE){
struct Player drafted;
printf("Welcome to the 2012 Draft Day Program\n");
get_name (&drafted);
printf("NAME_MAIN: %s\n", drafted.name);
get_position(&drafted);
printf("You've drafted %s at: %s\n", drafted.name, drafted.position);
get_age(&drafted);
get_bye_week(&drafted);
fputs("Would you like to draft another player?\n"
"Enter '1' for no, '0' for yes\n", stdout);
fflush(stdout);
if(fgets(text, sizeof text, stdin)){
int number;
if (sscanf(text, "%d", &number) == 1){
if (number == 1){
printf("Draft Ended!\n");
break;
}
}
}
}
return 0;
}
The resulting output is:
Welcome to the 2012 Draft Day Program
Enter Player Name: Aaron Rodgers
You've drafted: Aaron Rodgers
NAME_MAIN: Aaron Rodgers
nametemp: Aaron Rodgers
Enter Player Position in 'QB/RB/WR/TE/DEF' format: QB
NAME: QB
You've drafted QB at: QB1
You've drafted QB at: QB
Would you like to draft another player?
Enter '1' for no, '0' for yes
1
Draft Ended!
Why does drafted.name become "QB"?

Answer 1

In your get_name function you're assigning to the name field of your struct Player a stack variable name.
In this line:
drafted->name = name;
name is declared in the function and so it's scope is limited to that function. Once get_name returns, the variable goes out of scope, and attempts to use that memory invoke undefined behavior.
Instead of using the simple assignment, you need to allocate space for drafted->name using malloc, and use strncpy to make a copy of the name. If strdup is available, you can use that to allocate the space and do the copy in a single step. Alternately, you could allocate space for drafted->name before reading the name, and use it in place of the name variable.
As a final option, if you assume a maximum length for names - your current code allows names up to a string length of 19 - you can simply declare an array of that size for each struct Player:
struct Player
{
char name[NAME_MAXLEN];
You have an identical problem with your position field in the get_position function.