C Introduction

Question 1

Phases of compiling and running C programs

Answer 1

1) Program is created using editor and stored on disk
2) Preprocessor program processes the code
3) Compiler creates the object code and stores it on disk
4) Linker links object code with libraries, create .out and stores on disk
5) Loader puts program in memory
6) CPU takes each instruction and executes it, storing new data values as the program executes.

Question 2

Four types of files for compilers

Answer 2

• source code files
• header files
• object files
• binary executable files

Question 3

Source Code files

Answer 3

Contain function definitions.

Question 4

Header files

Answer 4

Contain function declarations, various preprocessor statements and allows source files to access externally-defined functions.

Question 5

Object files

Answer 5

The output of the compiler, and contains function definitions in binary form.
These are also not executable by themselves

Question 6

Binary Executable files

Answer 6

The output of the linker, and made from object files.
These can be directly executed.

Question 7

The Preprocessor (cpp or c preprocessor)

Answer 7

Before the C compiler starts compiling a source code file, the file is processed by the preprocessor.
Invoked automatically by compiler before compilation properly begins.
Converts source code files.

Question 8

Preprocessor commands

Answer 8

Start with a hashtag.

Question 9

include

Answer 9

Accesses function definitions defined outside the source code.

Question 10

define

Answer 10

Mainly defines constants.

Question 11

Other preprocessor examples

Answer 11

if

#else
#elif
#endif
#error

Question 12

The Compiler

Answer 12

After the preprocessor includes all header files and expands out all the preprocessor statements, the compiler then can compile the program.
Turns the source code file into an object code file, which contains the binary version of the source code, not the executable version.

Question 13

Invoking the compiler

Answer 13

May be invoked as either
% gcc foo.c
or
% gcc -c foo.c
This tells the computer to run the preprocessor on the file foo.c, and then compile it into an object file foo.o.

Question 14

-c

Answer 14

In the second example, -c means the we compile the source code into an object file but we do not invoke the linker.

Question 15

Invoking the compiler (one source code file):

Answer 15

% gcc foo.c -o foo
This tells the compiler to run the preprocessor on the file foo.c, compile, and link it to create an executable called foo.exe.

Question 16

-o

Answer 16

-o states the name of the output binary executable file.

Question 17

The Linker (ld)

Answer 17

Links object files together into a binary executable.
Is invoked automatically when using the compiler.

Question 18

Using the linker

Answer 18

% gcc foo.o bar.o baz.o -o myprogram

Question 19

Executing a file

Answer 19

% ./myprogram