String Support

String creation, cloning, assignment, and deletion. More...

Functions
char *	DDS_String_alloc (DDS_UnsignedLong length)
	Create a new empty string that can hold up to length characters.
char *	DDS_String_dup (const char *str)
	Clone a string. Creates a new string that duplicates the value of string.
void	DDS_String_free (char *str)
	Delete a string.
int	DDS_String_cmp (const char *s1, const char *s2)
	Compare two strings.
int	DDS_String_ncmp (const char *s1, const char *s2, DDS_UnsignedLong num)
	Compare two strings.
int	DDS_String_length (const char *string)
	Return the length of a string.

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Detailed Description

String creation, cloning, assignment, and deletion.

The functions in this class ensure consistent cross-platform implementations for string creation (DDS_String_alloc()), deletion (DDS_String_free()), and cloning (DDS_String_dup()) that preserve the mutable value type semantics. These are to be viewed as functions that define a string class whose data is represented by a 'char*'.

Conventions

The following conventions govern the memory management of strings in RTI Connext DDS Micro.

• The DDS implementation ensures that when value types containing strings are passed back and forth to the DDS APIs, the strings are created/deleted/assigned/cloned using the string class functions.
  • Value types containing strings have ownership of the contained string. Thus, when a value type is deleted, the contained string field is also deleted.
• The user must ensure that when value types containing strings are passed back and forth to the DDS APIs, the strings are created/deleted/assigned/cloned using the String class functions.

The representation of a string in C/C++ unfortunately does not allow programs to detect how much memory has been allocated for a string. RTI Connext DDS Micro must therefore make some assumptions when a user requests that a string be copied into. The following rules apply when RTI Connext DDS Micro is copying into a string or string sequence:

• If the 'char*' is NULL, RTI Connext DDS Micro will log a warning and allocate a new string on behalf of the user. To avoid leaking memory, you must ensure that the string will be freed (see Usage below).
• If the 'char*' is not NULL, RTI Connext DDS Micro will assume that you are managing the string's memory yourself and have allocated enough memory to store the string to be copied. RTI Connext DDS Micro will copy into your memory; to avoid memory corruption, be sure to allocate enough of it. Also, do not pass structures containing junk pointers into RTI Connext DDS Micro; you are likely to crash.

Usage

This requirement can generally be assured by adhering to the following idiom for manipulating strings.

     Always use
          DDS_String_alloc() to create,
          DDS_String_dup() to clone,
          DDS_String_free() to delete
      a string 'char*' that is passed back and forth between
      user code and the DDS C/C++ APIs.

Not adhering to this idiom can result in bad pointers, and incorrect memory being freed.

In addition, the user code should be vigilant to avoid memory leaks. It is good practice to:

• Balance occurrences of DDS_String_alloc(), DDS_String_dup(), with matching occurrences of DDS_String_free() in the code.
• Finalize value types containing strings. In C++ the destructor accomplishes this automatically. in C, explicit "destructor" functions are provided; these functions are typically called "finalize."

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Function Documentation

char* DDS_String_alloc

(

DDS_UnsignedLong

length

)

Create a new empty string that can hold up to length characters.

A string created by this function must be deleted using DDS_String_free().

This function will allocate enough memory to hold a string of length characters, plus one additional byte to hold the NULL terminating character.

Parameters:

length

<<in>> Capacity of the string.

Returns:

A newly created non-NULL string upon success or NULL upon failure.

char* DDS_String_dup

(

const char *

str

)

Clone a string. Creates a new string that duplicates the value of string.

A string created by this function must be deleted using DDS_String_free()

Parameters:

str	<<in>> The string to duplicate.

Returns:

If string == NULL, this function always returns NULL. Otherwise, upon success it returns a newly created string whose value is string; upon failure it returns NULL.

void DDS_String_free

(

char *

str

)

Delete a string.

Precondition:

string must be either NULL, or must have been created using DDS_String_alloc(), DDS_String_dup()

Parameters:

str	<<in>> The string to delete.

int DDS_String_cmp	(	const char *	s1,
		const char *	s2
	)

Compare two strings.

Precondition:

s1 and s2 can be NULL or non-NULL.

Parameters:

s1	<<in>> String 1 to compare.
s2	<<in>> String 2 to compare.

Returns:

0 if s1 equals s2, positive integer if s1 is greater than s2, negative integer if s1 is less than s2

int DDS_String_ncmp	(	const char *	s1,
		const char *	s2,
		DDS_UnsignedLong	num
	)

Compare two strings.

This function compares two strings for lexicographic equivalence, but only up to num bytes.

Parameters:

[in]	s1	<<in>> Left side of comparison
[in]	s2	<<in>> Right side of comparison
[in]	num	Maximum number of bytes to compare

Returns:

0 if s1 equals s2, positive integer if s1 is greater than s2, negative integer if s1 is less than s2

int DDS_String_length

(

const char *

string

)

Return the length of a string.

Precondition:

string must be non-NULL

Parameters:

string

<<in>> String to return length of

Returns:

length of string. Does not include the NUL-termination character. If a NULL value is passed as argument, RTI_SIZE_INVALID will be returned.