Agfdhyk

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("%sn", car);

    return newRacer;

}

This is the code I am running in my main to test it

Racer *t = make_racer("Tom", 4);

printf("%sn", t->graphic);

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("%sn", 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);

}