plhn plhn - 1 month ago 9
C++ Question

read 32bit integer from binary file

My binary file looks like this.

00000000: 0000 0803 0000 ea60 0000 001c 0000 001c
00000010: 0000 0000 0000 0000 0000 0000 0000 0000


left column is address.

I just tried to read
0000 0803
(=2051) as follows

ifstream if;
if.open("file");
uint32_t a;
if >> a;


As expected...It did not work :-(

a
was just 0 after execution.

I tried
long, int, unsigned int, unsigned long
. All failed.

Why these are not working and how can I achieve the goal?

Answer

You have two issues:

  1. Insuring you read the bytes you intend (no fewer, no more) from the stream.

    I'd recommend this syntax:

    uint32_t a;

    inFILE.read(reinterpret_cast<char *>(&a), sizeof(a));

  2. Insure you're interpreting those bytes with the correct byte order.

    Q: If you're on a PC, your CPU is probably little endian. Do you know if your data stream is also little-endian, or is it big endian?

    If the data is big-endian, I'd consider the standard networking functions to accomodate byte order: ntohl(), etc: http://www.retran.com/beej/htonsman.html

ALSO:

Follow Hcorg's and Daniel Jour's advice: don't forget about the "open mode" parameter, and don't forget to check for "file open" errors.

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