CODEWITHSUNDEEP
c++binaryfiles
Jerry Chou
Jerry Chou

Reputation: 302

Read zipped binary file in C++

I used to use popen(("zcat " + filename).c_str(), "r") to read zipped text files. However, I need read zipped binary file this time. I tried popen(("zcat " + filename).c_str(), "rb") but it failed as the return value is NULL even if the file does exist.

May I know why the way fails? I can guarantee the filename is properly defined, no special characters and the file does exist. The similar way works when I read zipped text files.

May I know what should be the correct way to do that?

Upvotes: 0

Views: 920

Answers (1)

Cornstalks
Cornstalks

Reputation: 38217

"rb" isn't a valid mode for popen. If you read the man page for popen, you'll see it says:

FILE *popen(const char *command, const char *type);

[...]

The type argument is a pointer to a null-terminated string which must contain either the letter 'r' for reading or the letter 'w' for writing.

[...]

If you look at the POSIX documentation for fopen, it says (regarding the mode string):

The character 'b' shall have no effect, but is allowed for ISO C standard conformance.

Thus, on a POSIX-ish system (like Linux), you don't need to specify binary mode when opening files, especially when using popen. Any FILE* you get back from popen will always be opened in binary mode.

If you decide to use zlib instead of popen("zcat", ...) (as other suggest, and I might recommend) there's a lot of good documentation, and I have personally found the zpipe.c demo very helpful.

Upvotes: 2

Related Questions