What does the "rcs" option in ar do?

c gcc static-libraries static-linking unix-ar
xiver77 picture xiver77 · Apr 18, 2015 · Viewed 21.3k times · Source

I did read the man file but it does not help. "rcs" seems to be the most popular option to pass to ar, but the meaning isn't so clear to me.

So "c" means to create a new archive, but then why use "r"? which seems to stand for "replace"? What will the "s" option do to the output?

Answer

Thomas Dickey picture Thomas Dickey · Apr 18, 2015

Reading the manual page (for ar) is a good start:

c

Create the archive. The specified archive is always created if it did not exist, when you request an update. But a warning is issued unless you specify in advance that you expect to create it, by using this modifier.

r

Insert the files member... into archive (with replacement). This operation differs from q in that any previously existing members are deleted if their names match those being added.

s

Write an object-file index into the archive, or update an existing one, even if no other change is made to the archive. You may use this modifier flag either with any operation, or alone. Running "ar s" on an archive is equivalent to running ranlib on it.

Comparing with POSIX, you may notice one difference: GNU ar makes the "-" prefixing options optional in itself.

An archive can contain other items than object-files (though this is not done often). Archives containing object-files require additional maintenance (e.g., done by ranlib) to make them usable by the linker.

According to the Rationale in POSIX ar, the -s option originated in BSD (System V did this automatically). However, running ranlib by itself is the prevailing practice (-s is rarely used). Interestingly enough, POSIX does not have ranlib, and ultimately the -s option will replace ranlib in the multitude of makefiles which were written to run on a variety of platforms.

Related questions

How to compile a static library in Linux?

I have a question: How to compile a static library in Linux with gcc, i.e. I need to compile my source code into a file named out.a. Is it sufficient to simply compile with the command gcc -o …

Read More
gcc will not properly include math.h

Here is a minimal example outlining my problem test.c: #include <stdio.h> #include <math.h> main () { fmod ( 3, 2 ); } And here is the command I am issuing to compile test.c gcc -lm test.c -o test …

Read More
Contents of a static library

I have a static library, say mystaticlib.a. I want to see its contents, such as the number of object files inside it. How can I do this on gcc?

Read More