Based on:
main.cpp:2:10: fatal error: cryptlib.h: No such file or directory
And:
gcc main.cpp ./cryptopp700/libcryptopp.a
Your directory structure looks like:
+- Project Folder
  |
  +- main.cpp
  |
  +- cryptopp700
    |
    +- cryltib.h
    +- ...
    +- libcryptopp.a
You should only need to add cryptopp700/ to your include header search path with -I:
g++ main.cpp -I ./cryptopp700 ./cryptopp700/libcryptopp.a
Note that you should also use g++ (the C++ compiler), not gcc (the C compiler).
You can also install the library since it has been built. By default it installs into /usr/local with:
skylake:cryptopp$ sudo make install
[sudo] password for jwalton:
install -m 644 *.h /usr/local/include/cryptopp
install -m 644 libcryptopp.a /usr/local/lib
install cryptest.exe /usr/local/bin
install -m 644 TestData/*.dat /usr/local/share/cryptopp/TestData
install -m 644 TestVectors/*.txt /usr/local/share/cryptopp/TestVectors
You can install into an alternate location using PREFIX:
skylake:cryptopp$ sudo make install PREFIX=/opt/local
install -m 644 *.h /opt/local/include/cryptopp
install -m 644 libcryptopp.a /opt/local/lib
install cryptest.exe /opt/local/bin
install -m 644 TestData/*.dat /opt/local/share/cryptopp/TestData
install -m 644 TestVectors/*.txt /opt/local/share/cryptopp/TestVectors
Then, you would change you compile and link command to something like:
g++ main.cpp -I /usr/local/include/cryptopp -o main.exe /usr/local/lib/libcryptopp.a
After an install like shown below, I normally tell folks to run the self tests. Unfortunately, the won't work if all you did was a make -j 4 or similar.
$ make -j 4
...
$ sudo make install
[sudo] password for jwalton:
install -m 644 *.h /usr/local/include/cryptopp
install -m 644 libcryptopp.a /usr/local/lib
install cryptest.exe /usr/local/bin
install -m 644 TestData/*.dat /usr/local/share/cryptopp/TestData
install -m 644 TestVectors/*.txt /usr/local/share/cryptopp/TestVectors
Here's the error you would get:
skylake:cryptopp$ cd /opt/local/bin/
skylake:bin$ ./cryptest.exe v
Using seed: 1544189072
Testing Settings...
passed:  Your machine is little endian.
passed:  Aligned data access.
passed:  sizeof(byte) == 1
passed:  sizeof(word16) == 2
passed:  sizeof(word32) == 4
passed:  sizeof(word64) == 8
passed:  sizeof(word128) == 16
passed:  sizeof(hword) == 4, sizeof(word) == 8, sizeof(dword) == 16
passed:  cacheLineSize == 64
hasSSE2 == 1, hasSSSE3 == 1, hasSSE4.1 == 1, hasSSE4.2 == 1, hasAVX == 1, hasAVX2 == 1, hasAESNI == 1, hasCLMUL == 1, hasRDRAND == 1, hasRDSEED == 1, hasSHA == 0, isP4 == 0
...
SHA validation suite running...
Exception caught: Can not open file TestVectors/sha.txt for reading
My thinking is things should "just work" for you. You should not need to worry about CRYPTOPP_DATA_DIR for a common case. And you certainly should not have to RTFM to make the common case work. That tells me there's a defect in our engineering process.
We are going to fix that now: Issue 760, Make self-tests run after install by a typical user.