4.5 Name Space Rules

ISO C defines several name spaces (see ISO/IEC 9899:1994 6.1.2.3). The same name could be used in a separate name space for a completely different item.

Name spaces are defined as:

  • label names

  • tags of structures, unions and enumerators

  • Members of structures or unions

  • All other identifiers.

Note: Name space and scope are not synonymous. Name space rules do not apply to scope. Scope is described in "Scoping Rules".

4.5.1 Names shall be used consistently within the same type.

For example, structure tags may only be reused as structure types, and union tags may be reused only for union types.

typedef struct MyStruct {
int one;
int two;
int three;
} MY_STRUCT;

Because of the similarity of MyStruct to MY_STRUCT, they may only be used to refer to the same structure type.

4.5.2 No identifier in one name space may be reused as an identifier in another name space

Exceptions are structure member and union member names.

typedef struct StructOne {
INT32 one;
INT16 two;
struct StructOne *MySelf;
} STRUCT_ONE;
typedef struct StructTwo {
INT16 one;
INT8 *two;
struct StructTwo *MySelf;
} STRUCT_TWO;
typedef struct {
STRUCT_ONE *StructOne; // NOT ALLOWED
STRUCT_TWO *StructTwoPtr; // ALLOWED, it is unique
} BAD_STRUCT;

4.5.3 A typedef name shall be a unique identifier.

The name that appears at the end of a typedef (STRUCT_ONE and STRUCT_TWO in the example in Section 4.5.2) is known as a typedef name. Because of ambiguity in the C specifications, and to avoid confusion, and once a typedef name is used in a structure declaration, it may not be declared elsewhere

Note: Including the declaration in a header file that is then included in a number of files is not a violation of this rule.

4.5.4 A tag name shall be unique.

The name after the struct in structure definitions (StructOne and StructTwo in the example in 4.5.2) is known as a structure tag or simply a tag. To avoid confusion, once a tag is used for declaring a structure it shall not be declared elsewhere.

Note: Including a header file that contains a structure definition is not a violation of this rule.

4.5.5 Prefix module-scope identifiers for cleaner namespaces.

The use of prefixes is not an absolute requirement, but has been shown as a successful method of avoiding namespace pollution and makes it easier to meet other naming requirements. A useful prefix is the module's name. For example, the UEFI Shell uses the prefix "Shell" for its identifiers.

SHELL_FREE_NON_NULL (Buffer);
ShellCommandLibConstructor (ImageHandle, SystemTable);