CLEAR C/C++ Development Environment Guide

GCC 9.3.1

GCC 9.3.1 is available on the CLEAR systems. It is not the system default, so the appropriate environment must be enabled before using this version of GCC or G++.

Quick Start

To enable GCC 9.3.1 for your current terminal session, run:

source /opt/rh/devtoolset-9/enable

You can verify the active compiler version with:

gcc --version

For the C++ compiler, use:

g++ --version

Per Session or Terminal

After establishing an SSH session to a CLEAR system, run:

source /opt/rh/devtoolset-9/enable

This sets the required PATH and environment variables for the current terminal session. If you open another SSH session or close and reopen your terminal, you must run the command again.

Compiling an Application

The following example creates and compiles a simple C program.

Create a file named hello.c:

cat > hello.c <<'EOF'
#include <stdio.h>

int main(void)
{
    printf("Hello, world!\n");
    return 0;
}
EOF

Create a build script named build-app.sh:

cat > build-app.sh <<'EOF'
#!/usr/bin/env bash

# Enable verbose output when started with:
# DEBUG=true ./build-app.sh
[[ ${DEBUG} ]] && set -xvu

# Enable GCC 9.3.1
source /opt/rh/devtoolset-9/enable

CC='gcc'
# CC='g++'  # Uncomment to use G++

${CC} --version

cc_opts="-Wall"

# Compile the application
${CC} ${cc_opts} hello.c -o hello
EOF

Make the script executable:

chmod u+x build-app.sh

Run the build script:

./build-app.sh

For verbose shell output, you can instead run:

DEBUG=true ./build-app.sh

After the application compiles successfully, run it with:

./hello

You should see:

Hello, world!

This example demonstrates the basic process. More complex projects can use tools such as make and project-specific Makefiles while the appropriate compiler environment is enabled.

Permanent Configuration

For most students, enabling the compiler environment only when needed is recommended. This helps prevent one course or project from affecting another.

If you need to determine your current login shell, run:

echo $SHELL

If you choose to configure the compiler environment automatically, add the following command to the appropriate shell initialization file:

source /opt/rh/devtoolset-9/enable

Be aware that permanently enabling a specific compiler version may affect other coursework or applications that expect the system-default compiler.

GCC 11.5.0

GCC 11.5.0 is available as a parallel compiler installation on the CLEAR systems. This allows users to access an alternate GCC and G++ toolchain without replacing the compiler supplied by the operating system.

Using the Compiler Wrapper Scripts

Wrapper scripts ending in -SCL are available to simplify access to the alternate compiler environment.

Examples:

gcc-SCL <options>
gcc-SCL --version

g++-SCL <options>
g++-SCL --version

Starting a Shell Session

You can also start a Bash shell with the appropriate development toolset enabled:

exec scl enable devtoolset-13 'bash'

After entering the enabled shell environment, the standard compiler commands can be used directly:

gcc <options>
gcc --version

g++ <options>
g++ --version

This approach may be useful when compiler tools, linkers, debuggers, or other related development utilities need to operate within the same environment.

Additional Documentation

For additional information about GCC Toolset and C/C++ development on Red Hat Enterprise Linux, see the Red Hat GCC Toolset documentation.

Clang 11.0.1

Clang 11.0.1 is available on the CLEAR systems. It is not the system default, so the appropriate environment must be enabled before using this version of Clang.

Quick Start

To enable Clang 11.0.1 for your current terminal session, run:

source /opt/rh/llvm-toolset-11.0/enable

Verify the active compiler version with:

clang --version

For the C++ compiler, use:

clang++ --version

Per Session or Terminal

After establishing an SSH session to a CLEAR system, run:

source /opt/rh/llvm-toolset-11.0/enable

This enables the required environment variables for the current terminal session. If you open another SSH session or close and reopen your terminal, you must run the command again.

Compiling an Application

The following example creates and compiles a simple C program using Clang.

Create a file named hello.c:

cat > hello.c <<'EOF'
#include <stdio.h>

int main(void)
{
    printf("Hello, world!\n");
    return 0;
}
EOF

Create a build script named build-app.sh:

cat > build-app.sh <<'EOF'
#!/usr/bin/env bash

# Enable verbose output when started with:
# DEBUG=true ./build-app.sh
[[ ${DEBUG} ]] && set -xvu

# Enable Clang 11.0.1
source /opt/rh/llvm-toolset-11.0/enable

CC='clang'
# CC='clang++'  # Uncomment to use Clang++

${CC} --version

cc_opts="-Wall"

# Compile the application
${CC} ${cc_opts} hello.c -o hello
EOF

Make the script executable:

chmod u+x build-app.sh

Run the build script:

./build-app.sh

For verbose shell output, you can instead run:

DEBUG=true ./build-app.sh

After the application compiles successfully, run it with:

./hello

You should see:

Hello, world!

Permanent Configuration

For most students, enabling the Clang environment only when needed is recommended. This helps prevent compiler settings from affecting other courses or applications.

If you choose to configure the Clang environment automatically, add the following command to the appropriate shell initialization file:

source /opt/rh/llvm-toolset-11.0/enable

Be aware that permanently enabling a specific compiler environment may affect applications that expect the system-default compiler.