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Naming Standards
C Language Standards


Types are distinctly different from instances, but it's possible to choose name so it's hard to know whether something is a type or a variable. Naming conflicts can occur between types and variables and even between types and functions.

Type names are always given _t suffix.


If a type is defined in a header file, there's a possibility its name will conflict with the name of another type defined elsewhere.

All types defined inside header files must have a prefix.

Types defined inside implementation (.c) files don't need a prefix. They have file scope, and imported types will have prefixes, so naming conflicts are highly unlikely.

The prefix (if any) must be all lower-case.


After the prefix (if any), the rest of the type name must be in CamelCase, beginning with an uppercase character.

// Inside a .c file:
typedef size_t ObjectCount_t;

// Inside the Sierra Wireless "Foo" component's API .h file:
typedef size_t swi_foo_ObjectCount_t;

Cardinal Types

Cardinal types (e.g., int, uint, int32, bool) are exempt from having a prefix or suffix because:

  • naming a variable "bool" or "int" won't be very descriptive, so there's little point to include those.
  • most cardinal types are built into the language and we're not allowed to change their names (and we wouldn't want to-imagine the confusion and the 3rd-party integration problems!).

Enumeration Members

Enumeration members are constants used in a similar way to macro constants. To clearly identify them as literal constants, they must be named using all upper-case with underscores separating words.

Also like macros, names of enumeration members can also conflict with the names of macros and enumeration members defined in include files from other modules. Any members of enumerations exported to other modules must have a prefix. Even members of enumerations only used within a single file should have a prefix if the names are likely to conflict with names defined in standard C libraries or other included code that doesn't use prefixes.

Struct and Union Namespaces

When a structure or union is defined, it's possible to give a name to that structure or union within a separate namespace. This example uses "MessageBody" and "Message" in the union and struct namespaces, but "MessageBody_t" and "Message_t" are not:

typedef union MessageBody
Request_t request;
Response_t response;
typedef struct Message
MessageType_t type;
MessageBody_t body;

All names in the struct namespace must be preceded by the keyword "struct". All names in the union namespace must be preceded by the keyword "union". This way, there's no confusion, and they're in a separate namespace so there's no possibility of naming conflicts with identifiers outside the namespaces. That's why these names are exempt from having an "_t" suffix. Athough if these are defined in a header file, they still need a prefix to prevent naming conflicts with other identifiers defined by other components in the same namespace.

Struct and Union Members

The names of members of structures and unions must start with a lower-case letter and use CamelCase to separate words.

Because structure and union member names are always used in context (in a dereference expression), there's no confusing them with other types' members (assuming the structure or union reference identifier is well named). No prefix is needed on structure or union member names:

typedef struct
char* textBufferPtr;
int textLength;
static void PrintTextBuffer(MyStructure_t* objectPtr)
int i;
for (i = 0; i < objectPtr->textLength; i++)
Only stack variable names and struct/union member names can (and must) start with lower-case letters.

Copyright (C) Sierra Wireless Inc. Use of this work is subject to license.