What's the Difference Between a Header File and a Library

What is the difference between a library file and a header file or are they synonymous?

Both are header files.

The first header file provides declarations of some of the functions provided by the C standard library. Therefore, one could say that it is part of the C standard library.

The second header file probably provides declarations of functions that are defined in other parts of your program. Therefore, it is not part of a library.

A library generally provides header files so that you can #include them in your program, so that the compiler has the necessary function declarations in order to call the functions in the library. However, the main part of the library, which consists of the actual function definitions, is not imported by the compiler, but rather by the linker.

What's the difference between a header file and a library?

Think of both like this (Disclaimer: this is a really high-level analogy ;) ..

The header is a phone number you can call, while...
...the library is the actual person you can reach there!

It's the fundamental difference between "interface" and "implementation"; the interface (header) tells you how to call some functionality (without knowing how it works), while the implementation (library) is the actual functionality.

Note: The concept is so fundamental, because it allows you flexibility: you can have the same header for different libraries (i.e. the functionality is exactly called in the same way), and each library may implement the functionality in a different way. By keeping the same interface, you can replace the libraries without changing your code.

And: you can change the implementation of the library without breaking the calling code!

What are Header Files and Library Files?

Generally, a header file notifies the compiler of certain things (mostly their existence or declarations) so that the compiler can correctly build a single translation unit (such as a single C file).

A library file is the actual executable code that does the work as specified in that header file. This is linked in by the linker to provide the actual functionality (the _definitions rather than just the declarations).

So, in your example, you may have the line:

#include <pthread.h>

which tells the compiler all about the existence of the pthread_mutex_this, pthread_condvar_that and pthread_thread_the_other stuff but doesn't actually provide the implementations of those things.

The -lpthread option tells the linker that it should locate a library based on the pthread name from which it can pull in the actual implementations, in order to forn the final executable.

Similarly, while stdio.h holds information about the I/O stuff, the actual code for it will be in the runtime library (though you rarely have to link that library specifically since the compiler will try to take care of it for you). Because you usually link with the compiler (i.e., the compiler invokes the linker for you), it knows that you're probably going to need the C run time library. If you were to use the linker directly (such as by using the ld command), that probably wouldn't happen, and you'd have to be explicit.

What's the relationship between header files and library files in c++?

A header file (usually) only contains declarations for classes and functions. The actual implementations are built from CPP files. You can then link against those implementations with only the header declarations available.

What is the basic difference between namespace , library and header files?

Namespace

A namespace is a declarative region that provides a scope to the identifiers (the names of types, functions, variables, etc) inside it. Namespaces are used to organize code into logical groups and to prevent name collisions that can occur especially when your code base includes multiple libraries.

Library

In programming, a library is a collection of precompiled routines that a program can use. The routines, sometimes called modules, are stored in object format. Libraries are particularly useful for storing frequently used routines because you do not need to explicitly link them to every program that uses them.

Header Files

Header files contain definitions of Functions and Variables, which is imported or used into any C++ program by using the pre-processor #include statement. Header file have an extension ".h" which contains C++ function declaration and macro definition.

thanks

What is the difference between a module and a header file?

I think you meant libraries and modules For example: 'import csv') which is usually found in the beginning of your Python code. You can include them in the program with the "import " just like header files in C++. So the difference is Libraries are a collection of modules written in C or Python and a module is a file containing Python definitions and statements. The file name is the module name with the suffix .py appended.