C Video Tutorial 8
Welcome to part 8 of my C Video Tutorial. In this video I cover a topic I have received many requests for. This is basically a C Malloc Tutorial.
Malloc() ( Memory Allocator ) is used to dynamically set aside memory at run time. Because malloc() returns a pointer to that location in memory it can be a bit confusing. I’ll cover how to store both regular data types as well as structs using malloc().
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Code From the Video
CTutorial8_1.c
#include <stdio.h>
#include <stdlib.h>
// When you define an int, float, or array, you define exactly how
// much memory you need and that is all you can get at run time
// using traditional data types.
// If you need to allocate memory as a program runs you need
// malloc()
// When malloc() is called you pass it the amount of memory required and
// it returns the address to that memory that you can refer to using
// a pointer. If the space couldn't be found null is returned.
int main(){
int amtOfNumbersToStore;
printf("How many numbers do you want to store: ");
scanf("%d", &amtOfNumbersToStore);
// Create an int pointer and set aside enough space to hold the ints
// required.
// pRandomNumbers points to just the first element, but it can
// access the others.
// The typecast (int *) isn't required in C, but is in C++
int * pRandomNumbers;
pRandomNumbers = (int *) malloc(amtOfNumbersToStore * sizeof(int));
// Check if memory was located by malloc
if(pRandomNumbers != NULL){
int i = 0;
printf("Enter a Number or Quit: ");
// Receives ints until the memory allocated is full, or
// until a non int is entered
// You store values by referring to the pointer using
// array notation
while(i < amtOfNumbersToStore && scanf("%d",
&pRandomNumbers[i]) == 1){
printf("Enter a Number or Quit: ");
i++;
}
printf("\nYou entered the following numbers\n");
//
for(int j = 0; j < i; j++){
printf("%d\n", pRandomNumbers[j]);
}
}
// Make sure you give back the memory allocated by malloc
// when you are finished with it.
free(pRandomNumbers);
// In this program free() isn't required because all allocated
// memory is returned to the system when the program terminates.
// free() would be required though if you were allocating large
// blocks of memory over and over without returning it.
// Let's say you store 10k of data using malloc, use it and have
// no further use for it but don't use free.
// Then you grab another 10k over and over. Eventually you'll
// run out of memory and get a memory leak.
return 0;
}
CTutorial8_2.c
#include <stdio.h>
#include <stdlib.h>
// struct that holds product information
struct product {
float price;
char productName[30];
};
int main(){
// Pointer to a struct
struct product *pProducts;
int i, j;
int numberOfProducts;
printf("Enter the Number of Products to Store: ");
// Dynamically we are defining how much space we need at run time
scanf("%d",&numberOfProducts);
// Allocates the memory required to store the structs
// Type casting isn't needed for C, but is required for C++
pProducts = (struct product *) malloc(numberOfProducts *
sizeof(struct product));
for(i=0; i < numberOfProducts; ++i){
printf("Enter Product Name: ");
// This time I use pointer arithmetic to cycle through the data
// and print it out
scanf("%s", &(pProducts+i)->productName);
printf("Enter Product Price: ");
scanf("%f", &(pProducts+i)->price);
}
printf("Products Stored\n");
for(j=0; j < numberOfProducts; ++j){
printf("%s\t%.2f\n", (pProducts+j)->productName, (pProducts+j)->price);
}
free(pProducts);
return 0;
}
Pretty sweet videos, brother.
My favourite text editor is Sublime Text 2. I know hardcore people that have dropped Emacs or Vim for Sublime so it’s definitely worth taking a look at!
Keep up the good work!
Many thanks from South Africa!
Thank you 🙂 I’m amazed by how popular I am in South Africa. That is very cool! I’ll have to check out Sublime Text. It looks very nice.
derek, your tutorial is a bit fast for starter but they are great!
Thank you 🙂 Yes I like to make videos unlike what else is out there. I’m the fast tutorial guy I guess.