C Header Files, Libraries, and Makefiles

Question 1

What should header (.h) files contain?

Answer 1

include statements for standard header files, common #define’s, structure definitions, typedefs, and function prototypes.

Question 2

What should NOT be in header (.h) files?

Answer 2

Function definitions and executable code.

Question 3

What is the standard naming convention for header files?

Answer 3

The header (.h) file is ALWAYS named after the code (.c) file it belongs to.

Question 4

What is a function prototype?

Answer 4

A declaration of a function that specifies its name, return type, and parameter types, but not its body.

Question 5

What is the purpose of the extern keyword in function prototypes?

Answer 5

It indicates that the function is defined elsewhere (typically in a .c file) and is globally visible.

Question 6

What is a well-structured approach to organizing C program files?

Answer 6

Split code into multiple files: header files (.h) containing declarations and prototypes, and implementation files (.c) containing function definitions.

Question 7

What problem can occur when including the same header file multiple times?

Answer 7

Redefinition errors for structures, typedefs, and other definitions.

Question 8

How can you visualize the problem with multiple includes?

Answer 8

When a file includes two other files that both include the same header file, that header file’s contents get included twice.

Question 9

What is the solution to the multiple includes problem?

Answer 9

Use #include guards in every header file.

Question 10

What is the syntax for #include guards?

Answer 10

ifndef __HEADER_NAME_H

#define __HEADER_NAME_H
/* content of header file */
#endif

Question 11

What naming convention should be used for #include guard identifiers?

Answer 11

Double-underscore, followed by the file name in capitals, with dots replaced by underscores (e.g., __STACK_H).

Question 12

What happens if you don’t use #include guards?

Answer 12

Compiler will generate “redefinition” errors for structures, typedefs, and other definitions.

Question 13

What is the command to compile a C file without linking?

Answer 13

gcc -c filename.c

Question 14

What is the command to link object files into an executable?

Answer 14

gcc file1.o file2.o -o programName

Question 15

What are the steps to compile a modular C program?

Answer 15

1) Compile each .c file into object files separately, 2) Link the object files together to create the executable.

Question 16

What is a library in C programming?

Answer 16

A collection of object files grouped together into a single, searchable unit.

Question 17

What are the two main types of libraries in C?

Answer 17

Static libraries (.a) and dynamically linked shared object libraries (.so).

Question 18

What are static libraries (.a)?

Answer 18

Libraries that are linked with and become part of the application at link time, resulting in larger but portable executables.

Question 19

What are dynamically linked shared object libraries (.so)?

Answer 19

Libraries that are linked to at runtime, resulting in smaller executables, but the shared object library must be available at execution.

Question 20

How do you link a program to the math library?

Answer 20

Use the -lm flag during linking: gcc myMaths.o -lm -o myMaths

Question 21

Why might this code fail to link: gcc myMaths.o -o myMaths?

Answer 21

If the code uses math functions like cosf(), it needs to be linked to the math library with -lm.

Question 22

What is the naming convention for libraries?

Answer 22

Libraries are named lib<name>.a for static libraries or lib<name>.so for shared libraries, but are linked using the -l<name> flag.</name></name></name>

Question 23

What is the purpose of a Makefile?

Answer 23

To automate the compilation and linking process, especially for projects with multiple source files and dependencies.

Question 24

What are the three main components of a Makefile rule?

Answer 24

Targets, dependencies, and commands.

Question 25

What is a target in a Makefile?

Answer 25

The file to be created or the action to be carried out.

Question 26

What are dependencies in a Makefile?

Answer 26

Files that the target depends on, which must exist and be up-to-date before the target can be built.

Question 27

What are commands in a Makefile?

Answer 27

The shell commands to execute to create the target from its dependencies. (Must be indented with tabs, not spaces.)

Question 28

How would you declare variables in a Makefile?

Answer 28

Using assignments like CC = gcc and CFLAGS = -ansi.

Question 29

How do you reference variables in a Makefile?

Answer 29

Using the $(variable_name) syntax, e.g., $(CC) $(CFLAGS) -c file.c

Question 30

What does the make command do?

Answer 30

It reads the Makefile, checks the dependencies, and executes the commands to build the targets that are out of date.

Question 31

What happens when you run make without specifying a target?

Answer 31

It builds the first target in the Makefile (the default target).

Question 32

What is the purpose of the touch command in relation to makefiles?

Answer 32

It updates a file's modification time, which can be used to trigger recompilation of dependent files.

Question 33

How does make determine if a target needs to be rebuilt?

Answer 33

It compares the modification times of the target and its dependencies. If any dependency is newer than the target, the target is rebuilt.

Question 34

What is the purpose of the clean target in a Makefile?

Answer 34

To remove all generated files (object files, executables) so that the project can be built from scratch.

Question 35

What are implicit rules in a Makefile?

Answer 35

Built-in rules that make knows about, such as how to create a .o file from a .c file.

Question 36

What is a phony target in a Makefile?

Answer 36

A target that doesn't represent a file but rather an action to be performed, like clean

Question 37

How would you write a Makefile rule to compile a .c file into a .o file?

Answer 37

file.o: file.c file.h $(CC) $(CFLAGS) -c file.c

Question 38

What would happen if you run make myProgram after modifying stack.h?

Answer 38

All files that depend on stack.h (directly or indirectly) would be recompiled, and the executable would be relinked.