I am implementing a OpenSSL code and have already included required header files but still I am getting errors like *

undefined reference to SSL_library_init

I guess it's a linking error rather than a compilation error.

I am implementing it in Linux box using slickeditor.

5 Answers

Link against libssl and libcrypto. Your LDFLAGS and LDLIBS would be as follows. Order matters for LDLIBS:

LDFLAGS = -L/usr/local/ssl/lib LDLIBS = -lssl -lcrypto 

Don't worry about adding the "lib" in front of library name, or the "so" or "a" suffix. The linker will do it for you.

If you are building from the command line, then you would use the following. Again, order matters.

gcc foo.c -o foo.exe -L/usr/local/ssl/lib -lssl -lcrypto 

If you are using the system's OpenSSL, then you can omit -L/usr/local/ssl/lib.

For me this meant to install

 apt install libssl1.0-dev 

These methods are deprecated in OpenSSL 1.1. You don't need to use it more. You can just remove it. More info in OpenSSL manual.

Simply add -lssl -lcrypto to your Makefile and it should work.

Example of Makefile:

foo: foo.o g++ -std=c++17 -o foo foo.cpp -lcrypto -lssl 

ldd libssl.so -> libcrypto.so.1.1 => not found

sudo ln -s /usr/local/lib64/libcrypto.so.1.1 /usr/lib64/libcrypto.so.1.1

libcrypto.so.1.1 => /lib64/libcrypto.so.1.1 (0x00007f17d46c7000)

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