Array of structs: function passing

[warsame]

I have an array of structs created with an initial size and filled with the members of the struct tag. as such

struct employee{
	
	char fullname[30];
	float salary;
	char fulldate[40];
};

struct employee my_employee[MAXSIZE]= {

    {"Johnson, larry", 233333.3, "December, 4th 1999\n"},
	 {"Kobe, Bryant", 90999.23, "September, 3rd, 1922\n"},
	 {"Lebron, James", 43334.43, "January, 5th 1932"},
	 {"Jermaine, O'neal", 5556677.4, "January, 5th 1932"},
	 {"Dwayne, Wade", 55556.4, "January, 7th 1932"}
	 
 }; 

Then i want to use that array (my_employee in a function) that will add another struct and print all the details in the struct.
HERE IS MY CODE // WHY WONT THIS WORK

void add_employee(struct employee  my_employee[]){
	int i;
	my_employee = malloc(200);
	struct employee *tempRecs;
	tempRecs = (struct employee *)malloc((size+1)*sizeof(struct employee));
	memcpy(tempRecs, my_employee, size*sizeof(struct employee));	
	for(i = 0; i < size; i++) {
		tempRecs[i] = (my_employee)[i];

			}
	
	
	printf("Please Enter Employee Full name:\n");
	scanf("%s", tempRecs->fullname);
	printf("Please Enter Employee salary");
	scanf("%f", &tempRecs->salary);
	printf("Please Enter Current Date (Month, DayYear)");
	scanf("%s", tempRecs[size].fulldate);
	size++;
	free( my_employee);
    my_employee = tempRecs;

}

[CommonTater]

It's about scoping and where variables are valid and not... Think about passing a pointer to an employee struct instead of the struct itself...

[laserlight]

Then i want to use that array (my_employee in a function) that will add another struct and print all the details in the struct.
HERE IS MY CODE // WHY WONT THIS WORK

I think that you are over-complicating the code. You do not need to use malloc and free here. Rather, keep track of the number of elements of the struct employee array that are in use. Pass that number (or a pointer to the variable) as an argument to add_employee, which can then simply copy over the values for the next struct employee object.

[Jamdog]

What is this line doing?

my_employee = malloc(200);

As far as I can see, it would cause you to lose the contents of my_employee every time add_employee is called.

[warsame]

i am using malloc because i want to only create enough space for just
one struct everytime add_employee is called. as far as using a struct employee
pointer to point to my array of structs the following code gives me an
error:
[code]

struct employee *mainDatabase;
mainDatabase = &myEmployee[0]; // i want to start at the first struct in
array of structs and if increase mainDatabse++ that hopefully will give me
the next struct in my array of structs??

how do i use a pointer in my add_employee fucntion to create 4 bytes of pointer space when it is used??

add_employee(struct employee *my_employee) // is this correct?

[grumpy]

You can't have your cake and eat it too.

malloc() and free() do not provide a means to magically resize an array that was declared and defined at compile time.

The basic rule is that free(ptr) is invalid unless ptr is a value returned by malloc() [or a related function].

Your code - indirectly - passes a pointer to free() that was not returned by malloc(). Hence it is invalid.

Either provide MAXSIZE with a value that is larger than your code will ever need (which is essentially what laserlight described) or ensure your array is malloc()'ed BEFORE you ever attempt to free() it.

[lvl99]

I'm not sure if I'm really helping but this is how I would solve it. I tried to simplify it.

#include <stdio.h>
#include <string.h>

struct employee{
    char fullname[30];
    float salary;
    char fulldate[40];
};

int main (void){
  int i;
  struct employee *my_employee[MAXSIZE]; 

  struct employee add_employee(char *name, float salary, char *date ){
	struct employee temp;
        strcpy(temp.fullname,name);
        temp.salary=salary;
        strcpy(temp.fulldate,date);
        return temp;
  };


  // add employee info
  for(i = 0; i < MAXSIZE; i++)
     
    my_employee[i]=(struct employee)malloc(sizeof(struct employee));
    
    // returns a struct
    //get arguments using scanf()
    my_employee[i]=add_employee(<pass arguments >);

    //print data
    //free memory 

    return 0;
}

[warsame]

so if i dont use a struct array but instead create something like this

struct employee my_employee = {

    "Johnson, larry", 233333.3, "December, 4th 1999	
	 
 }; 
struct employee *tempRecs;
tempRecs = &my_employee; // this line gives me the error " conflicting types for 
tempRecs"

i now want to have one struct and keep adding to this struct by allocating space and copying over elements every time. is this possible?

[lvl99]

I'll try and help , but post the exact and complete code that you are using to get that particular error.

[grumpy]

You either want to have a struct, or you want to have an array of structs.

An array of X is something different from an X.

If you want to have one struct that you "add to", you are expecting an X to act as if it is a (resizable) array of X. Or you want to be allowed to act as if it is.

Such requirements are muddled and ambiguous. And one requirement when programming a computer is that you specify things unambiguously. A computer does not handle ambiguity well.

[warsame]

ITS SEEMS I HAVE CONFUSED MYSELF,
i have posted all of my code here. i simply want to have a pointer to a struct that
will allocate space when called accordingly and a temporary struct pointer that will serve as
my new struct which will copy all the values in the struct and the user added struct to then update my print struct function. HERE IS MY FULL CODE

#include <string.h>
#define MAXSIZE 5
int size =0;
struct employee{
	
	char fullname[30];
	float salary;
	char fulldate[40];
};
struct employee *tempRecs;
struct employee my_employee = {

    "Johnson, larry", 233333.3, "December, 4th 1999"

 }; 




void print_records(){

	struct employee *mainDatabase = &my_employee;

	printf("\nFull Name: '%s'\n", mainDatabase->fullname);
	printf("Salary: $%.2f\n" , mainDatabase->salary);
	printf("Date Hired: %s\n", mainDatabase->fulldate);
	mainDatabase++;
}

void add_employee(struct employee  **my_employee){
	int i;
	struct employee *tempRecs;
	my_employee = (struct employee **)malloc((size + 1)*sizeof(struct employee *));

	tempRecs = (struct employee *)malloc((size+1)*sizeof(struct employee));
	memcpy(tempRecs, my_employee, size*sizeof(struct employee));	
	for(i = 0; i < size; i++) {
		tempRecs[i] = (*my_employee)[i];

			}
	
	
	printf("Please Enter Employee Full name:\n");
	scanf("%s", tempRecs->fullname);
	printf("Please Enter Employee salary");
	scanf("%f", &tempRecs->salary);
	printf("Please Enter Current Date (Month, DayYear)");
	scanf("%s", tempRecs[size].fulldate);
	size++;
	free( *my_employee);
    *my_employee = tempRecs;

}

[lvl99]

where is main()? And you should add

 #include <stdlib.h>

since you are using the malloc() function.

[Adak]

I liked your first idea - make MAXSIZE something BIG - maybe 200 or so, and use the static array idea, instead of malloc() and realloc(). Your program will keep track of how many records are active in your database, all the time. Add a record, the count goes up by one, delete a record, and you decrement the count by one, as well.

When you delete a person, don't delete them - just zero out their name and/or ID number or both. (You have to watch it, there WILL be people with duplicate names).

Now your display and add functions know that anyone with a zeroed out name and ID, will not be displayed for normal searches, and are available to put a new record, right into that space.

Leave malloc() and realloc() out of it, until you have a bit more C under your belt. I hear you saying "but what am I going to do when I run out of space?".

Simple, you read in another 200 names from the data file, and carry on, like before. No, it's not perfect, but you can NEVER hold all the records in a database, in main memory, unless it's rather tiny. Using malloc and realloc will help, but they usually only put off the inevitable - you have to be able to read your records, from a source other than main memory - sooner or later.

[warsame]

I liked your first idea - make MAXSIZE something BIG - maybe 200 or so, and use the static array idea, instead of malloc() and realloc(). Your program will keep track of how many records are active in your database, all the time. Add a record, the count goes up by one, delete a record, and you decrement the count by one, as well.

When you delete a person, don't delete them - just zero out their name and/or ID number or both. (You have to watch it, there WILL be people with duplicate names).

Now your display and add functions know that anyone with a zeroed out name and ID, will not be displayed for normal searches, and are available to put a new record, right into that space.

Leave malloc() and realloc() out of it, until you have a bit more C under your belt. I hear you saying "but what am I going to do when I run out of space?".

Simple, you read in another 200 names from the data file, and carry on, like before. No, it's not perfect, but you can NEVER hold all the records in a database, in main memory, unless it's rather tiny. Using malloc and realloc will help, but they usually only put off the inevitable - you have to be able to read your records, from a source other than main memory - sooner or later.

i have actually solved this problem without using malloc and reaalloc, i know want to use these two and ignore file system reading for the moment, i am trying to learn the machine architecture of the c language and need help to allocate memory for a pointer, copy all current records to that pointer using a loop and then set the pointer free().... and so on.

[Adak]

i am trying to learn the machine architecture of the c language and need help to allocate memory for a pointer, copy all current records to that pointer using a loop and then set the pointer free().... and so on.

You can't "copy all current records to that pointer", because a pointer (any pointer), can only hold ONE address. You mean "copy all current records into a block of allocated memory the array points to".

First thing, is you need to include stdlib.h if you want to use malloc(). Also, you should have stdio.h included, as well.

Did you add in main() function, yet?

Add that, and then report what your errors are.