C programming compilers are programs that translate C source code into executable code for a specific platform. They perform various tasks such as lexical analysis, syntax analysis, semantic analysis, code optimization, and code generation.
Two different compilers may produce different results from a C program because of several reasons. One reason is that some aspects of the C language are implementation-defined or undefined, meaning that the compiler can choose how to handle them. For example, the order of evaluation of function arguments is unspecified, so different compilers may evaluate them in different orders and produce different side effects. Another reason is that different compilers may have different target platforms, which may have different sizes of basic data types, different memory layouts, different instruction sets, etc. Therefore, it is important to write portable and standard-compliant C code that does not rely on compiler-specific behavior.
The best C compiler depends on various factors such as the target platform, the performance, the features, the compatibility, the cost, etc. There is no definitive answer to this question, as different compilers may have different advantages and disadvantages for different situations. Some of the popular C compilers are GCC, Clang, Visual Studio, Turbo C, etc.
Compiling a C program involves writing the source code in a text editor, saving it with a .c extension, and invoking the compiler with the appropriate options and arguments. The compiler will then check the syntax and semantics of the code, optimize it if possible, and generate an executable file or an object file that can be linked with other files or libraries. The exact steps may vary depending on the compiler and the platform.
Compiling and running a C program are two separate steps. Compiling converts the source code into executable code while running executes the code on the target platform. To run a C program, one needs to have access to the executable file and any required libraries or dependencies. The executable file can be run directly from the command line or from an IDE (Integrated Development Environment) that provides a graphical interface.
The compilation process in a C program consists of several phases that transform the source code into executable code. The phases are:
- Preprocessing: This phase performs macro expansion, file inclusion, conditional compilation, and other textual transformations on the source code.
- Lexical analysis: This phase converts the preprocessed source code into a sequence of tokens that represent keywords, identifiers, literals, operators, etc.
- Syntax analysis: This phase analyzes the structure and grammar of the token sequence and builds a parse tree that represents the syntactic structure of the program.
- Semantic analysis: This phase checks the meaning and validity of the parse tree and performs type checking, scope resolution, constant folding, etc. It also annotates the parse tree with additional information such as types, values, addresses, etc.
- Intermediate code generation: This phase converts the annotated parse tree into an intermediate representation that is independent of the source language and the target platform. The intermediate representation can be in various forms such as abstract syntax tree (AST), three-address code (TAC), quadruples, triples, etc.
- Code optimization: This phase improves the quality and efficiency of the intermediate code by applying various techniques such as dead code elimination, loop optimization, common subexpression elimination, constant propagation, etc.
- Code generation: This phase translates the optimized intermediate code into machine code or assembly code for the target platform. It also performs tasks such as register allocation, instruction selection, instruction scheduling, etc.
- Linking: This phase combines the generated code with other object files or libraries to produce an executable file.
The C compiler phases are also known as compiler passes or compiler stages. Another name for the C program compiler is C translator. A cross compiler is a compiler that produces executable code for a different platform than the one on which it runs. For example, a cross compiler can run on a Windows machine and produce executable code for a Linux machine or an embedded device. Cross compilers are useful for developing software for platforms that have limited resources or capabilities.
–save-temps
C Programming -save-temps is a GCC option that instructs the compiler to store the intermediate files that are normally deleted after the compilation process. These files include:
- The preprocessed source file (.i or .ii), which contains the source code after macro expansion, conditional compilation, and inclusion of header files.
- The assembly file (.s), which contains the assembly code generated by the compiler for the target architecture.
- The object file (.o), which contains the binary code produced by the assembler.
Using this option can be useful for debugging purposes, as it allows you to inspect the intermediate stages of the compilation process and see how your source code is transformed into executable code. For example, you can use the -save-temps option to see how a macro is expanded, or how a function is translated into assembly instructions.
To use the -save-temps option, you need to pass it as an argument to GCC along with your source file and any other options you want to use. For example, if you have a file called hello.c that contains a simple C program, you can compile it with -save-temps using this command:
gcc -save-temps hello.c -o hello
This will create four files in the current directory: hello.c, hello.i, hello.s, and hello.o. The last one is the executable file that you can run. The other three are the intermediate files that you can examine with a text editor or a tool like objdump.
Note that in GCC 4.5 and later, you can also use the -save-temps=obj option, which saves the intermediate files in the same directory as the output file. This can help avoid name conflicts when you have multiple source files with the same name in different directories.
