Using namespace std in c pdf book

This section lists the namespaces that the application will be using frequently, and saves the programmer from specifying a fully qualified name every time that a method that is contained within is used. Same as cin and cout, string is also defined in the std namespace. It is an alternative to explicit namespace reference inline within your code. To use strings in this way, we need to include the header since it is declared in the. By the way, if you only need a few distinct functions, you can tell it just that. Consider this, there are two students in one classroom having same name for example vishal. However, despite its popularity, c was not without its shortcomings. Lets discuss these two ways of creating string first and then we will see which method is better and why.

It puts the names of its members in a distinct space so that they dont conflict with the names in other namespaces or global namespace. Sometimes we need to execute a block of statements only when a particular condition is met or not met. The idea of namespaces is quite common in computing languages. After editing by nathan, it is obvious that string isnt sufficient for your prototype. The keyword using technically means, use this whenever you can. Basically, a namespace is a special area inside which something is defined. Data types this program demonstrates variables, literal constants, and data types. Just like int, float or other data types, we can use string data type also. Alternatively, we can specifically point out that its only these two symbols we want to avoid typing std in front of. You can also avoid prepending of namespaces with the using namespace directive.

A namespace is like a context which determines the meaning of a symbol if you think of it as a space where names are stored, you wont be too far wrong. For accessing the class of a namespace, we need to use namespacenameclassname. The standard requires that you specify which names in a standard header file youll be using. Simplest is to put all using declarations at the top of the file, after the includes, but outside of any namespaces. If we compile and run above code, this would produce the following result. Strings are words that are made up of characters, hence they are known as sequence of characters. Using using how to use the std namespace david kieras, eecs department, university of michigan febrary 2015 why namespaces. Brian kernighan and dennis ritchie introduced c to the wider programming world with their book the c programming language. This phone book will only store peoples name and phone numbers.

A namespace definition begins with the keyword namespace followed by the namespace. Among the members you find the cout stream, which is the standard output stream in. An example of this is the std namespace which is declared in each of the header files in the standard library. Their first program in the book simply printed hello, world. As giblit has already said, using using namespace std. Std is the standard namespace cout, cin and a lot of other things are defined in it. The compiler joins the parts together during preprocessing and the resulting namespace contains all the members declared in all the parts.

Aug 27, 2017 this feature is not available right now. Maybe this is a bit overkill if were only using cout and endl out of the std namespace. This directive tells the compiler that the subsequent code is making use of names in the specified namespace. We can use using keyword so that we dont have to use complete name all the time. All exercies soon to be completed this repertory is an active development record of my programming skills.

The c language is peculiar because it is a highlevel language with many of the features of a lowlevel language. This means that one way to call them is by using std cout and std cin. After typing this in visual studio, the intellisense window will automatically open, displaying what the namespace contains. Names introduced in a using directive obey normal scope rules. In general, avoid putting using directives in header files. The compiler hasnt a clue what that type is, as std. After you write this instruction, if the compiler sees string it will know that you may be referring to std string, and if it sees vector, it will know that you may be referring to std vector. This can cause name collisions because it adds every name in the std namespace to the global namespace. The result of 0 0 0 is too large to be stored in an int variable n. This is what happens if a using declaration is put into a namespacedefinition. For example, if you only plan on using cout and endl, there is no need to use the entire std namespace.

March 16, 2016 question 2 what is the output of the following program. These identifiers can be classes, functions, objects, variables, constants etc. The std namespace has tons of identifiers, many of which are. Now a question comes in your mind that what is a namespace. Using declaration within a function or struct or class or nested block. Or, you could include the using namespace std statement and then code. Identifiers outside the namespace can access the members by using the fully qualified name for each identifier, for example std vector std string vec. This is what happens if a using declaration is put into a namespace definition. A namespace can be declared in multiple blocks in a single file, and in multiple files. Read here for why after editing by nathan, it is obvious that string isnt sufficient for your prototype. For a small program like this one its unlikely that youll run into any problems then again, maybe not but its best to get into the habit of using the std prefix on names in the std namespace. Cpp programming tutorial pdf book for beginner techringe. The namespace is thus implied for the following code. This is called decision making, as we are executing a certain code after making a decision in the program logic.

When programs get very large and complex, and make heavy use of libraries from a variety of sources, the possibility of name. In many programming languages, a namespace is a context for identifiers. So, in this case, cout is defined in std namespace. When programs get very large and complex, and make heavy use of libraries from a variety of sources, the possibility of name collisions rears its incredibly annoying head. Lets start with std cout std short form of standard is a namespace and cout is defined in this std namespace. David sherrill school of chemistry and biochemistry. All declarations within those blocks are declared in the named scope.

But using std all the time can sometimes produce rather cluttered code if you e. While most compilers now accept the new format, they dont require it. Multiple namespace blocks with the same name are allowed. To use strings in this way, we need to include the header since it is declared in the header. By using namespace or the using namespace keyword, one is offered a clean way to aggregate code under a shared label, so as to prevent naming collisions or just to ease recall and use of very specific scopes. All answers are my own and represent my work to the best of my ablity. Jump to navigation jump to search david cary 20100914. Let us rewrite our preceding example, with using directive. A namespace is a declarative region that provides a scope to the identifiers names of the types, function, variables etc inside it. C is somewhere in between the two extremes of a very. Submitted by doctorspeedcode on sunday, august 3, 2014 23. From wikibooks, open books for an open world programming.