What is the gcc command in Linux with examples

The gcc command in Linux is used to invoke the GNU Compiler Collection to compile C programs. It is one of the most widely used compilers for C and C++.

Here is a detailed guide with examples:

Syntax

• [source_file]: The C source file to be compiled.
• [options]: Additional options to control the compilation process.
• [output_file]: The name of the generated executable file (using the -o option).

Basic Usage

1. Compile a C Program

Compile a single file and create an executable:

• program.c: The source file to compile.
• -o program: Specifies the name of the output executable (program).

Example:

2. Compile and Run Without Specifying Output File

If you omit the -o option, the output executable will be named a.out by default:

3. Compile Multiple Source Files

If your program consists of multiple source files, compile them together:

Example:

Common GCC Options

4. Enable Debugging Information

Use the -g option to include debugging information in the executable (useful for debugging with gdb):

5. Optimize the Code

Use the -O flag to optimize the compiled code. Common levels are:

• -O0: No optimization (default).
• -O1: Basic optimization.
• -O2: Moderate optimization.
• -O3: Aggressive optimization.

Example:

6. Compile Without Linking

The -c option compiles the source file into an object file (.o) without producing an executable:

This generates an object file named program.o.

7. Link Object Files

After creating object files with the -c option, link them together to create an executable:

8. Specify the Standard

You can specify the C standard (e.g., C89, C99, C11) using the -std flag:

9. Suppress Warnings

Use the -w option to suppress warnings during compilation:

10. Show All Warnings

Use the -Wall option to enable most warning messages:

Examples of GCC Commands

Example 1: Basic Compilation

Compile a simple “Hello, World” program:

Compile and run:

Example 2: Debugging with gdb

Compile with debugging information:

Run the executable in gdb:

Example 3: Using -c for Separate Compilation

1. Create two source files:
   • main.c:
     c

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     #include <stdio.h>
void hello();
int main() {
hello();
return 0;
}

   • hello.c:
     c

     CopyEdit

     #include <stdio.h>
void hello() {
printf("Hello from another file!\n");
}

2. Compile each file into an object file:
   bash

   CopyEdit

   gcc -c main.c
gcc -c hello.c

3. Link the object files into an executable:
   bash

   CopyEdit

   gcc main.o hello.o -o program
./program


Common Errors and Troubleshooting

1. Error: gcc: command not found
   • Install GCC using your package manager:
     • Debian/Ubuntu: sudo apt install gcc
     • Red Hat/CentOS: sudo yum install gcc
2. Warnings About Implicit Declarations
   • Always include headers like <stdio.h> for functions like printf.
3. Segmentation Fault
   • Compile with -g and debug with gdb to identify the issue.

Conclusion

The gcc command is a versatile tool for compiling C programs in Linux. With options like -o, -g, -Wall, and -std, you can customize the compilation process to fit your needs. Let me know if you’d like more advanced examples or debugging tips!