Namespaces How Shall I Name Thee Why Namespaces
- Slides: 7
Namespaces How Shall I Name Thee?
Why Namespaces by default, function, class, global constant and variable scope is global in large programming projects multiple people may give different constructs the same name, resulting in name collision. words like sort, find, count and print are tempting name collision may result in compile-time error - when header is included linker error namespaces– designed to sub-divide global scope and avoid name collision
Defining Namespaces define a namespace block, declare constructs inside namespace my. Namespace{ const int limt=5; void my. Func(int a){ ++a; } } functions, classes, etc. (constructs with separate definitions) may be defined outside namespace my. Namespace{ const int limt=5; void my. Func(int); } void my. Namespace: : my. Func(int a){ ++a; } thus structured, the namespace is non-executable and should go into a header file
Employing Namespaces several styles always employ scope resolution operator (explicit statement of scope) for(int i=0; i < my. Namespace: : limit; ++i) my. Namespace: : my. Func(i); import a name – specify that you are employing a specific name in this file using my. Name. Space: : limit; using my. Name. Space: : my. Func; for(int i=0; i < limit; ++i) my. Func(i); import all names in a namespace using namespace my. Namespace; for(int i=0; i < limit; ++i) my. Func(i); do not do in headers – opens namespace for all source files including this header
Scope of Importing variables can be imported either into global scope or into a block importing into the global scope – imported variables can be used anywhere using my. Name. Space: : limit; int main(void){ for(int i=0; i < limit; ++i) my. Func(i); } importing into the scope of a function – imported variables can be used inside function only int main(void){ using my. Name. Space: : limit; for(int i=0; i < limit; ++i) my. Func(i); }
std has an extensive set of names used in programs. Contains cout, cin, endl, vector, string, etc. three styles of employing std: explicit scope resolution of all names – pro: safest – con: program code becomes less terse employ using with specific names – pro: more terse – con: have to maintain name list at beginning of the file employ using namespace std; – pro: simplest, tersest – con: unexpected names are imported: sort, find, count are in std; do not use in header files!
Review Questions what is the scope of a function? global variable? global constant? what is a namespace and why is it needed? how to define a namespace? is namespace an executable statement? how do you define a function declared in a namespace? the three styles of employing namespaces are explicit statement namespace importing specific name importing all names in a namespace how do you employ each style? what are the advantages/disadvantages of each style? which style should be employed in a header what happens when using is put inside/outside a function definition?
