Function to write two bytes at a time to a file?

First, two bytes are read and combined at a time from a file, so 7F FF (two separate values) becomes one value, 7FFF. That part has already been done. However, I'm looking for a means of injecting those bytes into a new file. I've tried fputc, but that only injects one character at a time. I've also tried fputs, but that only works for strings; the values are stored as integers in this case.

Any tips for injecting these double-byte values into a file? Help is much appreciated!

How do you assemble say 0x7FFF out of two bytes 0x7F and 0xFF - using << and | perhaps (or *256 and add)

Simply pick it apart in the reverse way, and write some bytes.

Is the file to be text or binary? If it's a binary file, use fwrite...

Cprogramming.com - Tutorials - C File I/O

Kevin

Quote:

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Originally Posted by Flotonic

First, two bytes are read and combined at a time from a file, so 7F FF (two separate values) becomes one value, 7FFF. That part has already been done. However, I'm looking for a means of injecting those bytes into a new file. I've tried fputc, but that only injects one character at a time. I've also tried fputs, but that only works for strings; the values are stored as integers in this case.

Any tips for injecting these double-byte values into a file? Help is much appreciated!

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Look at fprintf() in your library documentation...

If you have the 2 byte value in a short int you can easily print it to the file as decimal, hex, or octal.
If it's in a string you can just print it directly to the file.

Really... this isn't hard.

Salem and kmess were more understanding of how the question was asking about binary stuff, not text. Thanks for the tips!

Quote:

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Originally Posted by Flotonic

Salem and kmess were more understanding of how the question was asking about binary stuff, not text. Thanks for the tips!

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In that case just use fread() and fwrite()...

Just finished giving fwrite(); a shot. I get "passing argument 1 of fwrite makes pointer from integer without a cast." I think that fwrite is made for putting down down things declared with "char," not "int."

I could always try making a loop to split each value into two smaller values that can fit into single-spaced "char" variables.

fwrite expects you to tell it where it is, not what it is. (EDIT: At the same time, it also expects you to be using data types that make sense. If you only want to write two bytes out to a file, then using a four-byte data type will be Frowned Upon. If you have to write a specific number of bytes, then a char array is probably your best option.)

Quote:

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Originally Posted by Flotonic

Just finished giving fwrite(); a shot. I get "passing argument 1 of fwrite makes pointer from integer without a cast." I think that fwrite is made for putting down down things declared with "char," not "int."

I could always try making a loop to split each value into two smaller values that can fit into single-spaced "char" variables.

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Try it like this...

Code:

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short myint;

fwrite(&myint, sizeof(myint), file);

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fWrite wants the address not the value.

EDIT: Sorry Tabstop... I didn't see your post till after sending this...

Quote:

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Originally Posted by Flotonic

I've tried fputc, but that only injects one character at a time. I've also tried fputs, but that only works for strings; the values are stored as integers in this case.

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Why does it matter if you call fputc twice or fwrite once?


Quzah.

What matters is that fwriting two bytes at once exposes you to endian issues.

Quote:

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Originally Posted by Salem

What matters is that fwriting two bytes at once exposes you to endian issues.

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It sounds like he has that covered though:

Quote:

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Originally Posted by Flotonic

First, two bytes are read and combined at a time from a file, so 7F FF (two separate values) becomes one value

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He already knows the order he needs to read them, so writing them should be the same exercise in reverse. It's not like he's going to magically make this portable by writing two bytes at once instead of one at a time.

I'm just not sure why writing one byte two times confused him more than reading one byte two times.


Quzah.