Windows core programming-function Return Error

1. Windows program error handling mechanism

Windows API return type

Data Type	Indicates the value of failure.
V o I d	The operation of this function cannot fail. The Return Value Type of the WI n d o w s function is rarely v o I D.
B o l	If the function fails to run, the returned value is 0. Otherwise, the returned value is not 0. It is best to test the returned value to determine whether it is 0 or not. Do not test whether the returned value is t r u e
H A n d l e	If the function fails to run, the return value is generally n u L. Otherwise, the return value is H a n d l e, which is used to identify an object that you can operate on. Note that some functions return a handle value I n valid _ handle_va L U E, which is defined as-1. The Platform SDK documentation of the function will clearly show whether n u l or I n va l I d _ H a n d l e _ va l I D is returned when the function fails to run.
P v o I d	If the function fails to run, the return value is n u L; otherwise, p v o I D is returned to identify the memory address of the data block.
L o n g/d w o r d	This is an unhandled value. The return number function usually returns l o n g or d w o r d. If, for some reason, the function cannot count the objects to be counted, the function usually returns 0 or-1 (depending on the function ). If the called function returns l o n g/d w o r d, read the Platform SDK documentation carefully to ensure that potential errors are correctly checked.

The WI n e r o r. h header file contains a list of error codes defined by m I c r o s o f t. Each error has three representations, for example:

// Messageid: error_path_not_found
// Messagetext:
// The system cannot find the path specified.
# Define error_path_not_found 3l

When an error occurs, you can use the following function to obtain the error ID,
DWORD getlasterror ();
You can also use the following function to obtain the corresponding text by ID:
DWORD formatmessage (
DWORD dwflags, // source and processing options
Lpvoid lpsource, // pointer to message source
DWORD dwmessageid, // requested message identifier
DWORD dwlanguageid, // language identifier for requested message
Lptstr lpbuffer, // pointer to message buffer
DWORD nsize, // maximum size of Message Buffer
Va_list * arguments // pointer to array of message Inserts
);
When an error occurs when an API is called, you can view the error using the following method immediately, but the subsequent API calls will overwrite the preceding errors.

Figure 1-1 in the wa t c h window of Visual Studio 6.0, type "@ e r, h r" to view the final error code of the current thread.

Visual Studio also has a small utility called error lookup. You can use error lookup to convert the error code number into the corresponding text description (see Figure 1-2 ).

You can also define your own error code, but you need to create a correct 32-bit ID. It cannot conflict with the system.

Table 1-2 error code fields

Bit	3 1 ~ 30	29	28	27 ~ 16	15 ~ 0
Content	Severity	M I c r o s o f t/customer	Retained	Device code	Exception Code
Description	0 = successful	0 = m I c r o s o f t company-defined code	Must be 0	Defined by m I c r o s o f t	Defined by Microsoft/customer
	1 = for Reference	1 = Customer-defined code
	2 = warning
	3 = Error