CODEWITHSUNDEEP
c
Sarkis
Sarkis

Reputation: 33

sizeof Char / Array length Memory allocation in C,

Can somebody tell me about the memory allocation in c? What is the size of a char variable? 2 or 4? Why the difference in the address value between 2 neighboring char elements in an array is only 1?

char foo [] = {'a', 'b'};
printf ("This is the Address of val1 %d \n", &foo[1]);           // -1079295441
printf ("This is the Address of val2 %d \n", &foo[2]);           // -1079295440
printf ("The size of each array member is %d \n", sizeof(foo));  // 2

Upvotes: 3

Views: 1070

Answers (2)

mpekim
mpekim

Reputation: 29

Memory Allocation is a bit tricky, but it's easier than you think. It is, as the name implies, the usage and selection of data to optimize program function and speed. Basically, Memory Allocation is a "perk" of languages such as C/C++ that allow programmers to only use EXACTLY as much data as needed, freeing up memory for other computer functions.

Some good info to know about memory...

  • memory is known in "bytes", these are 8-bit "groups" of data.
  • A "bit" is a value that is either 0 or 1.

Variable sizes:

  • Char: 1 byte
  • Int: 4 bytes
  • double: 8 bytes

When neighboring elements are of the same type (for example, an array of chars), they will have a difference in address that increments/decrements by the value of the memory size. Since a char variable has a size of 1 byte, neighboring elements will have addresses that differ by 1.

Ex: char addresses: 1204, 1205, 1206, 1207... (1 byte)

int addresses: 1204, 1208, 1212, 1216... (4 bytes)

Upvotes: 0

Sergey Kalinichenko
Sergey Kalinichenko

Reputation: 726479

You are not printing addresses correctly: an address is not an int, so you cannot use %d to print it. Use %p (for "pointer") instead, and cast the address to void* for printing:

printf ("This is the Address of val1 %p\n", (void*)&foo[1]);

Now your program produces this or similar output:

This is the Address of val1 0xffbd2fcf 
This is the Address of val2 0xffbd2fd0 
The size of each array member is 2

Two pointers are off by 1, which is the size of a single char. The size of the entire array is 2. If you want to print the size of a single element, use foo[0].

Upvotes: 3

Related Questions