OpenSSL link options -lssl and -lcrypto in GCC

Question

After adding the link options: -lssl and -lcrypto, my program was correctly compiled. However, I found GCC doesn't include the two options, so where do the options come from?

Solution

The GCC documentation tells us that -l is the option to link with a library.

-llibrary
-l library
Search the library named library when linking. (The second alternative with the
library as a separate argument is only for POSIX compliance and is not
recommended.)

So you're telling gcc to link with the libraries "ssl" and "crypto". These libraries are typically installed in /usr/lib. On Linux they'll be called libssl.so and libcrypto.so. On OS X they'll be called libssl.dylib and libcrypto.dylib.

Comments

[Matt Elson]

On Cygwin they'll be called libssl.a and libcrypto.a

[Hack06]

For static linking use additional parameters like this -static -lcrypto -lz -ldl -static-libgcc (source: stackoverflow.com/a/25811538/4410376)