Array of struct pointers and assigning struct data

Question

I have run into a problem or maybe I am just doing something wrong since I am new to C and structs. I want to take a text file such as this:

3
Trev,CS,3.5
Joe,ART,2.5
Bob,ESC,1.0

and read in the first line as the number of students then from there out gather student info and put them in a struct called StudentData:

typedef struct StudentData{
 
 char* name;
 char* major;
 double gpa;
 
} Student;

Where I run into a problem is after I seemingly assign the data to an individual struct, the struct data becomes mixed up. I have commented out exactly what is going on (or at least what I believe is). Hopefully it isn't painful to read.

main(){
 int size, i;
 char* line = malloc(100);
 scanf("%d\n", &size);//get size
 char* tok;
 char* temp;
 Student* array[size]; //initialize array of Student pointers
 for(i = 0; i<size;i++){
 array[i] = malloc(sizeof(Student));//allocate memory to Student pointed to by array[i]
 array[i]->name = malloc(50); //allocate memory for Student's name
 array[i]->major = malloc(30);//allocate memory for Student's major
 }
 
 for(i = 0; i<size;i++){
 scanf("%s\n", line);//grab student info and put it in a string
 tok = strtok(line, ","); //tokenize string, taking name first
 array[i]->name = tok;//assign name to Student's name attribute
// printf("%s\n",array[i]->name);//prints correct value
 line = strtok(NULL, ",");//tokenize
 array[i]->major = line;//assign major to Student's major attribute
// printf("%s\n",array[i]->major);//prints correct value
 temp = strtok(NULL, ",");//tokenize
 array[i]->gpa = atof(temp);//assign gpa to Student's gpa attribute
// printf("%.2f\n\n",array[i]->gpa); //prints correct value
 }
 
 for(i=0;i<size;i++){ //this loop is where the data becomes jumbled
 printf("%s\n",array[i]->name);
 printf("%s\n",array[i]->major);
 printf("%.2f\n\n",array[i]->gpa);
 }
}

The output looks like this:

Trev
Joe
3.50
Joe
Bob
2.50
Bob
ESC
1.00

I can't really understand what is going on in the memory between assigning values and printing them.

Answer 1

You can't use regular assignment with char * like that. You will need to use strcpy. For example:

strcpy(array[i]->name,tok);

Otherwise you are making all the array[i]->name point to the same string.

• Trevor Arjeski: how would i handle the string to double?