How to link OpenSSL library in macOS using gcc?

Question

I have OpenSSL installed through the Homebrew package manager. I have found the library and header files I need.

The headers are:

/usr/local/Cellar/openssl/1.0.2h_1/include/openssl
/usr/local/Cellar/openssl/1.0.2j/include/openssl
/usr/local/Cellar/openssl/1.0.2k/include/openssl

The library files are:

/usr/lib/libssl.0.9.7.dylib
/usr/lib/libssl.0.9.8.dylib
/usr/lib/libssl.dylib

I've tried several gcc commands to try to link the OpenSSL library, including:

gcc md5.c -I/usr/local/Cellar/openssl/1.0.2k/include -lssl
gcc md5.c -I/usr/local/Cellar/openssl/1.0.2k/include -llibssl
gcc md5.c -I/usr/local/Cellar/openssl/1.0.2k/include -llibssl.dylib
gcc md5.c -I/usr/local/Cellar/openssl/1.0.2k/include -llibssl.0.9.8
gcc md5.c -I/usr/local/Cellar/openssl/1.0.2k/include -llibssl.0.9.8.dylib

All of them produce either a "File not found" error or a linker error.

What's the proper way to do this?

Solution

It looks like you are trying to link against the openssl libraries installed with your os, rather than the homebrew libraries. Try to find where homebrew installed the 1.0.2k libraries.

find /usr/local/Cellar/ -name "libssl.*"

You should find something like /usr/local/Cellar/_path_of some_sort/libssl.a. Try to link against this library rather than the ones in /usr/lib. The /usr/lib libraries are old and not compatible with the header files you are using.

gcc md5.c -I/usr/local/Cellar/openssl/1.0.2k/include -L/usr/local/Cellar/path_of_some_sort/ -lssl -lcrypto -o md5

Comments

[Legend of Overfiend]

@thrig I found several: /usr/local/Cellar/openssl/1.0.2h_1/lib/pkgconfig/libcrypto.p‌​c /usr/local/Cellar/openssl/1.0.2h_1/lib/pkgconfig/libssl.pc /usr/local/Cellar/openssl/1.0.2h_1/lib/pkgconfig/openssl.pc /usr/local/Cellar/openssl/1.0.2j/lib/pkgconfig/libcrypto.pc /usr/local/Cellar/openssl/1.0.2j/lib/pkgconfig/libssl.pc /usr/local/Cellar/openssl/1.0.2j/lib/pkgconfig/openssl.pc /usr/local/Cellar/openssl/1.0.2k/lib/pkgconfig/libcrypto.pc /usr/local/Cellar/openssl/1.0.2k/lib/pkgconfig/libssl.pc /usr/local/Cellar/openssl/1.0.2k/lib/pkgconfig/op...

[Goodword]

Specifically, the following worked for me: gcc -Wall -g -L/usr/local/Cellar//[email protected]/1.1.0g/lib/ -I/usr/local/Cellar//[email protected]/1.1.0g/ -lcrypto -o urtorrent urtorrent.o bencode.o metainfo.c filestring.o