When accessing my graphic in my struct it prints an empty line - c

Question

Here is the struct that I am using.
#define MAX_CAR_LEN 12 ///< length does not include the trailing NUL byte
/// Racer_S structure represents a racer's row, position and display graphic.
typedef struct Racer_S {
int row; ///< vertical row or "racing lane" of a racer
int distance; ///< column of rear of car, marking its position in race
char *graphic; ///< graphic is the drawable text of the racer figure
} Racer;
When I call this function everything works fine inside it and creates everything correctly. I am able to access the row and distance fine. When I try and print the graphic I am printed an empty row in my terminal. I believe that this might be because "graphic" in the struct is a char* but I assign it a fixed sized array of char. When this function is called and passed in the name "Tom", graphic is supposed to be "~O=Tom----o>". I am new to C what am I doing wrong?
Racer * make_racer( char *name, int row ){
//Creating a newRacer instance
Racer *newRacer = malloc(sizeof(*newRacer));
newRacer->graphic = (char*)malloc(MAX_CAR_LEN);
char car[MAX_CAR_LEN] = "~O="; //"~O=-------o>"
char *pCar;
int length = strlen(name) + 2;
//Add the name after the engine of the car
for (int i = 0; i < length; ++i)
car[i+3] = name[i];
//Calculate the amount of dashes needed
int printDashes = 7 - strlen(name);
//add the extra dashes
for (int j = 1; j <= printDashes; ++j)
car[length + j] = '-';
// creates the end of the car
car[MAX_CAR_LEN-2] = 'o';
car[MAX_CAR_LEN-1] = '>';
pCar = strdup(car);
newRacer->row = row;
newRacer->distance = 0;
newRacer->graphic = &car[0];
// printf("%s\n", car);
return newRacer;
}
This is the code I am running in my main to test it
Racer *t = make_racer("Tom", 4);
printf("%s\n", t->graphic);

Answer 1

You have mentioned the below statement in your question.
This is the code I am running in my main to test it
acer *t = make_racer("Tom", 4);
printf("%s\n", t->graphic);
In make_racer function you have used a local charecter array variable called car and assigned the address to newRacer->graphic . This variable(char car[MAX_CAR_LEN+1] ;) memory goes out of scope after returning from the function.
Please refer this thread to understand more about the local scope in C.
Now to resolve your problem, In make_racer function you have to dynamically allocate memory for newRacer->graphic as well.
Racer * make_racer( char *name, int row ){
:
Racer *newRacer = malloc(sizeof(*newRacer));
newRacer->graphic = (char*)malloc(MAX_CAR_LEN+1);
:
//newRacer->graphic = &car[0]; # this is wrong.
strcpy(newRacer->graphic,car); //copy the content to allocated memory.
/*
* Warning:Just i am pointing out the issue here.
* strcpy may cause buffer over run.
* You have to use snprintf/strncpy family to prevent buffer overrun.
*/
}
Make sure you free the memory in your main.
int main() {
:
free(newRacer->graphic); //before free the momory for "newRacer"
free(newRacer);
}