Developer Experience of the AWS SDK for C++ Now Simplified by CMake

Building a cross-platform C or C++ project is tedious and time consuming. You often have to manage build files for each platform’s build system. On Unix-like systems, you might use Make, while on Windows you would have to use MSBuild. To make matters worse, in each of these build systems you have to manually maintain and configure compiler flags and linker flags.

We’re very pleased to announce that starting with version 1.0.109 of the AWS SDK for C++, you can more easily use CMake to build your project against the SDK. In addition, it’s easier to uninstall the SDK.

Here’s a simple example script that uses CMake to build a project against the SDK.

cmake_minimum_required(VERSION 2.8)
project(s3Encryption)
find_package(AWSSDK REQUIRED COMPONENTS transfer s3-encryption)
add_executable(s3Encryption s3Encryption.cpp)
target_link_libraries(s3Encryption ${AWSSDK_LINK_LIBRARIES})

To uninstall the SDK, just run make uninstall inside your build directory.

In earlier versions, each SDK had its own CMake scripts. However, the functionality only told you that the SDK existed. Now when you run sudo make install, this latest version installs a new directory named AWSSDK.

On a Unix-like system, this is the default installation path:
“/usr/local/lib/cmake/AWSSDK”

On Windows, this is the default installation path:
“C:/Program Files/aws-cpp-sdk-all/lib/cmake/AWSSDK”

Several CMake scripts are created in this directory. The most important one is AWSSDKConfig.cmake. CMake can use it to find the AWSSDK module and load the script. For information about naming of this specific file name, see CMake Find Package Config Mode.

Calling find_package(AWSSDK) makes several useful variables and macros available to you, as follows.

Variables:

AWSSDK_LIB_DIR
AWSSDK_BIN_DIR
AWSSDK_INCLUDE_DIR

Macros:

AWSSDK_CPY_DYN_LIBS(SERVICE_LIST CONFIG DESTDIR)
AWSSDK_LIB_DEPS(SERVICE DEPS)
AWSSDK_DETERMINE_LIBS_TO_LINK(SERVICE_LIST OUTPUT)

You can use the AWSSDK_CPY_DYN_LIBS macro to copy all the SDKs that are specified in the SERVICE_LIST. In addition, it copies all their dependent libraries (including recursive dependencies) and the core library to DESTDIR. You use CONFIG to specify the compile time binary configuration of the SDKs. You don’t have to set it, or you can set it to Debug, Release, and others.

For example, S3 encryption depends on Core, Amazon S3, and AWS KMS. Both S3 and KMS depend on Core. So, the following script copies libaws-cpp-sdk-core.so, libaws-cpp-sdk-s3.so, libaws-cpp-sdk-kms.so and libaws-cpp-sdk-s3-encryption.so to the current directory.

Set(SERVICE_LIST s3 s3-encryption)
AWSSDK_CPY_DYN_LIBS(SERVICE_LIST “” “./”)

You could use the AWSSDK_LIB_DEPS macro to output dependent libraries of SERVICE to DEPS. However, remember that SERVICE is just a single SDK’s name instead of a list of all the SDK names, and DEPS is a list of names of simplified libraries such as “core; s3; kms; s3-encryption”.

The AWSSDK_DETERMINE_LIBS_TO_LINK macro is similar to AWSSDK_CPY_DYN_LIBS. However, it doesn’t copy but does output the library names to OUTPUT. Notice that OUTPUT is a complete list of library names, which you could use as arguments of find_library(). For example, “aws-cpp-sdk-core; aws-cpp-sdk-s3;”.

The PkgConfig metadata file of each SDK is installed on all platforms under the same directory as CMake scripts. On Unix-like systems, we can use the PkgConfig module in CMake to simplify this, as we did in the previous example script. But if you want to try a command line build or a simple Makefile build, you can use a command like the following to generate all the flags, libs, and paths you want.

pkg_config –libs –cflags aws-cpp-sdk-s3-encryption

Try this sample project on your own platform. Before you begin, be sure to do the following:

• Install the latest version of the AWS SDK for C++.
• Create and set up AWS credentials on your test machine.
• Create an Amazon S3 bucket under your account. The region must be the same as the region used in your AWS client configuration.
• Create an AWS KMS master key.
• Apply changes to main.cpp in this project, such as master key ID, bucket name, key you wanted to use, and so on.

Please reach out to us with questions and improvements. As always, pull requests are welcome!