Chapter 2. Creating C or C++ Applications

1. Source files are compiled to object files.
2. Object files and libraries are linked (including the previously compiled sources).

Procedure

1. Change to the directory containing the source code file(s).

2. Run gcc with the -c option:

   $ gcc -c source.c another_source.c

   Copy to Clipboard Toggle word wrap

   Object files are created, with their file names reflecting the original source code files: source.c results in source.o.

   Note

   With C++ source code, replace the gcc command with g++ for convenient handling of C++ Standard Library dependencies.

Procedure

1. Compile and link your code with the -g option to generate debugging information:

   $ gcc ... -g ...

   Copy to Clipboard Toggle word wrap

2. Optional: Set the optimization level to -Og:

   $ gcc ... -g -Og ...

   Copy to Clipboard Toggle word wrap

   Compiler optimizations can make executable code hard to relate to the source code. The -Og option optimizes the code without interfering with debugging. However, be aware that changing optimization levels can alter the program’s behavior.

3. Optional: Use -g for moderate debugging information, or -g3 to include macro definitions:

   $ gcc ... -g3 ...

   Copy to Clipboard Toggle word wrap

Procedure

1. Change to the directory containing the object code file(s).

2. Run gcc:

   $ gcc ... objfile.o another_object.o ... -o executable-file

   Copy to Clipboard Toggle word wrap

   An executable file named executable-file is created from the supplied object files and libraries.

   To link additional libraries, add the required options after the list of object files.

   Note

   With C++ source code, replace the gcc command with g++ for convenient handling of C++ Standard Library dependencies.

Procedure

1. Create a directory hello-c and change to it:

   $ mkdir hello-c
   $ cd hello-c

   Copy to Clipboard Toggle word wrap

2. Create file hello.c with the following contents:

   #include <stdio.h>
   
   int main() {
     printf("Hello, World!\n");
     return 0;
   }

   Copy to Clipboard Toggle word wrap

3. Compile and link the code with GCC:

   $ gcc hello.c -o helloworld

   Copy to Clipboard Toggle word wrap

   This compiles the code, creates the object file hello.o, and links the executable file helloworld from the object file.

4. Run the resulting executable file:

   $ ./helloworld
   Hello, World!

   Copy to Clipboard Toggle word wrap

Procedure

1. Create a directory hello-c and change to it:

   $ mkdir hello-c
   $ cd hello-c

   Copy to Clipboard Toggle word wrap

2. Create file hello.c with the following contents:

   #include <stdio.h>
   
   int main() {
     printf("Hello, World!\n");
     return 0;
   }

   Copy to Clipboard Toggle word wrap

3. Compile the code with GCC:

   $ gcc -c hello.c

   Copy to Clipboard Toggle word wrap

   The object file hello.o is created.

4. Link an executable file helloworld from the object file:

   $ gcc hello.o -o helloworld

   Copy to Clipboard Toggle word wrap

5. Run the resulting executable file:

   $ ./helloworld
   Hello, World!

   Copy to Clipboard Toggle word wrap

Procedure

1. Create a directory hello-cpp and change to it:

   $ mkdir hello-cpp
   $ cd hello-cpp

   Copy to Clipboard Toggle word wrap

2. Create file hello.cpp with the following contents:

   #include <iostream>
   
   int main() {
     std::cout << "Hello, World!\n";
     return 0;
   }

   Copy to Clipboard Toggle word wrap

3. Compile and link the code with g++:

   $ g++ hello.cpp -o helloworld

   Copy to Clipboard Toggle word wrap

   This compiles the code, creates the object file hello.o, and links the executable file helloworld from the object file.

4. Run the resulting executable file:

   $ ./helloworld
   Hello, World!

   Copy to Clipboard Toggle word wrap

Procedure

1. Create a directory hello-cpp and change to it:

   $ mkdir hello-cpp
   $ cd hello-cpp

   Copy to Clipboard Toggle word wrap

2. Create file hello.cpp with the following contents:

   #include <iostream>
   
   int main() {
     std::cout << "Hello, World!\n";
     return 0;
   }

   Copy to Clipboard Toggle word wrap

3. Compile the code with g++:

   $ g++ -c hello.cpp

   Copy to Clipboard Toggle word wrap

   The object file hello.o is created.

4. Link an executable file helloworld from the object file:

   $ g++ hello.o -o helloworld

   Copy to Clipboard Toggle word wrap

5. Run the resulting executable file:

   $ ./helloworld
   Hello, World!

   Copy to Clipboard Toggle word wrap

Procedure

1. Compile the program source files with headers of the static library:

   $ gcc ... -Iheader_path -c ...

   Copy to Clipboard Toggle word wrap

   Replace header_path with the directory path containing the header files.

2. Link the program with the static library:

   $ gcc ... -Llibrary_path -lfoo ...

   Copy to Clipboard Toggle word wrap

   Replace library_path with the directory path containing the file libfoo.a.

3. Run the program:

   $ ./program

   Copy to Clipboard Toggle word wrap

Procedure

1. Change to the directory with library sources.

2. Compile each source file to an object file with the Position independent code option -fPIC:

   $ gcc ... -c -fPIC some_file.c ...

   Copy to Clipboard Toggle word wrap

   The object files have the same file names as the original source code files, but their extension is .o.

3. Link the shared library from the object files:

   $ gcc -shared -o libfoo.so.x.y -Wl,-soname,libfoo.so.x some_file.o ...

   Copy to Clipboard Toggle word wrap

   The used major version number is X and minor version number Y.

4. Copy the libfoo.so.x.y file to an appropriate location, where the system’s dynamic linker can find it. On Red Hat Enterprise Linux, the directory for libraries is /usr/lib64:

   # cp libfoo.so.x.y /usr/lib64

   Copy to Clipboard Toggle word wrap

   Note that you need root permissions to manipulate files in this directory.

5. Create the symlink structure for soname mechanism:

   # ln -s libfoo.so.x.y libfoo.so.x
   # ln -s libfoo.so.x libfoo.so

   Copy to Clipboard Toggle word wrap

Procedure

1. Create intermediate object files with GCC.

   $ gcc -c source_file.c ...

   Copy to Clipboard Toggle word wrap

   Append more source files if required. The resulting object files share the file name but use the .o file name extension.

2. Turn the object files into a static library (archive) using the ar tool from the binutils package.

   $ ar rcs libfoo.a source_file.o ...

   Copy to Clipboard Toggle word wrap

   File libfoo.a is created.

3. Use the nm command to inspect the resulting archive:

   $ nm libfoo.a

   Copy to Clipboard Toggle word wrap
4. Copy the static library file to the appropriate directory.

5. When linking against the library, GCC will automatically recognize from the .a file name extension that the library is an archive for static linking.

   $ gcc ... -lfoo ...

   Copy to Clipboard Toggle word wrap

Procedure

1. Create a directory hellomake:

   $ mkdir hellomake

   Copy to Clipboard Toggle word wrap

2. Change to the hellomake directory:

   $ cd hellomake

   Copy to Clipboard Toggle word wrap

3. Create a file hello.c with the following contents:

   #include <stdio.h>
   
   int main(int argc, char *argv[]) {
     printf("Hello, World!\n");
     return 0;
   }

   Copy to Clipboard Toggle word wrap

4. Create a file Makefile with the following contents:

   CC=gcc
   CFLAGS=-c -Wall
   SOURCE=hello.c
   OBJ=$(SOURCE:.c=.o)
   EXE=hello
   
   all: $(SOURCE) $(EXE)
   
   $(EXE): $(OBJ)
           $(CC) $(OBJ) -o $@
   
   %.o: %.c
           $(CC) $(CFLAGS) $< -o $@
   
   clean:
           rm -rf $(OBJ) $(EXE)

   Copy to Clipboard Toggle word wrap
   Important

   The Makefile recipe lines must start with the tab character! When copying the text above from the documentation, the cut-and-paste process may paste spaces instead of tabs. If this happens, correct the issue manually.

5. Run make:

   $ make

   Copy to Clipboard Toggle word wrap

   $ gcc -c -Wall hello.c -o hello.o
   $ gcc hello.o -o hello

   Copy to Clipboard Toggle word wrap

   This creates an executable file hello.

6. Run the executable file hello:

   $ ./hello

   Copy to Clipboard Toggle word wrap

   Hello, World!

   Copy to Clipboard Toggle word wrap

7. Run the Makefile target clean to remove the created files:

   $ make clean

   Copy to Clipboard Toggle word wrap

   # rm -rf hello.o hello

   Copy to Clipboard Toggle word wrap