gtpc2mfqC/C++ Language Support User's Guide

TO2_previous-Return the Previous Element

This function returns the previous element in the collection and points the cursor at the element. The definition of the previous element depends on the collection implementation.

Format

#include <c$to2.h>
TO2_BUF_PTR TO2_previous (const TO2_PID_PTR pid_ptr,
                                TO2_ENV_PTR env_ptr);

pid_ptr
The pointer to the cursor persistent identifier (PID) created by one of the TPF collection support (TPFCS) create cursor application programming interfaces (APIs).

env_ptr
The pointer to the environment as returned by the TO2_createEnv function.

Normal Return

For a normal return, this buffer contains a C header file followed by a copy of the data requested. The normal return is a pointer (TO2_BUF_PTR) to a structure (buffer) of type TO2_BUF_HDR (see Type Definitions).

Error Return

An error return is indicated by a zero. When zero is returned, use the TO2_getErrorCode function to determine the specific error code. For more information, see Error Handling.

The following error codes are common for this function:

TO2_ERROR_CURSOR

TO2_ERROR_EMPTY

TO2_ERROR_ENV

TO2_ERROR_EODAD

TO2_ERROR_METHOD

TO2_ERROR_PID

TO2_ERROR_ZERO_PID

Programming Considerations

Examples

The following example returns the previous element in the collection that the cursor points to and repositions the cursor to point to it.

#include <c$to2.h>                /* Needed for TO2 API Functions    */
#include <stdio.h>                /* APIs for standard I/O functions */
 
TO2_ERR_CODE     err_code;        /* TO2 error code value            */
TO2_ERR_TEXT_PTR err_text_ptr;    /* TO2 error code text pointer     */
TO2_BUF_PTR      buffer_ptr;
TO2_PID          cursor;
TO2_ENV_PTR      env_ptr;

  ·
  ·
  ·
/*********************************************************************/ /* Read the previous item that the cursor points to. */ /*********************************************************************/ if ((buffer_ptr = TO2_previous(&cursor, env_ptr)) == NULL) { err_code = TO2_getErrorCode(env_ptr); if (err_code != TO2_ERROR_EODAD) { printf("TO2_previous failed!\n"); process_error(env_ptr); } else { printf("TO2_previous successful!\n"); } }

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