Thanks Kyle, your patch is correctly directed.

I'm surprised that this line of code works :

char *input_filenames[argc];

argc is not a constant, so it looks like a kind of "dynamic size allocation on stack" .
I suspect that Visual will not like it.
Let's find out....

Quick question about error case behavior :

Let's suppose we want to compress a list of 6 filenames.
In the middle of the list, say name 3, compression fails (typically because the file does not exist or is not valid).
How should the program behave ?
=> Exit immediatly with an error code ?
=> Proceed with the rest of list, trying to compress as much valid files as possible ?

@Cyan4973, it's C99 feature "VLA" (Variable Length Array). Since our CFLAGS has -std=c99, it's strictly valid code. But VLA has some problems :

• As you suppose, VC++ and old C89 compilers could not compile it.
• VLA becomes optional feature in C11 and greater (see __STDC_NO_VLA__). 😧

If we will support C89 compilers, intermingled declarations also should be removed.

How should the program behave ?

Since this PR's intention is mimicing gzip, gzip-like behaviour will be expected. In this case, latter is more "gzip-like" behaviour. The following log is my experiment :

# Initial state
$ ls -1
lz4.1
lz4c.1
lz4cat.1

# Normal compression
$ gzip -k lz4.1 lz4c.1 lz4cat.1
$ ls -1
lz4.1
lz4.1.gz
lz4c.1
lz4c.1.gz
lz4cat.1
lz4cat.1.gz

$ rm *.gz

# Compression with errors
$ gzip -k lz4.1 dummy1 lz4c.1 dummy2 lz4cat.1 dummy3
gzip: dummy1: No such file or directory
gzip: dummy2: No such file or directory
gzip: dummy3: No such file or directory
$ ls -1
lz4.1
lz4.1.gz
lz4c.1
lz4c.1.gz
lz4cat.1
lz4cat.1.gz

Thanks Takayuki
It's an excellent reference.
Let's make it behave this way.

I'll also update Kyle contribution to make it C89 compatible.