Thread: Question about the function "read" of the ifstream class

Hello I have the following code:

Code:

ifstream file("file.data");
int number = 0;
file.read((char *)&number, sizeof(int));

I would like to understand what the third line does.

the read function reads a block of 4 bytes from the file "file.data".

the first argument specifies where we want to save that block of data.

in what format is the data going to be saved in this variable?

(char *) reminds me of an array of chars(bytes). So the block will be in bytes?

and why is there an "&" after that? I tried without it but it didn't work.

the & is the address of the variable "number"
and then it takes this address and casts it to a sequence of bytes

I don't really understand this

thanks in advance

the read function reads a block of 4 bytes from the file "file.data".

Correct, if sizeof(int) is 4 bytes.

in what format is the data going to be saved in this variable?

Since the variable is of an int type, it will write the data to this int variable.

(char *) reminds me of an array of chars(bytes). So the block will be in bytes?

This is a C style cast. The read function reads a series of bytes from the file and places them into the variable whose address you provide.

and why is there an "&" after that? I tried without it but it didn't work.

You must send the address of the variable to read, so it can alter the contents of this variable.

the & is the address of the variable "number"

Yes.

and then it takes this address and casts it to a sequence of bytes

No, it is saying take these 4 bytes and put them into the location that starts at the address of "number".

Jim

thanks a lot for the explanation