SWMM5 errormanager.c Summary

 Below is a step‐by‐step explanation of how errormanager.c works. It provides a simple runtime error interface using a small “error handle” object that can store and retrieve an error code, look up the associated message, and clear the error.

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1. Purpose

// Purpose: Provides a simple interface for managing runtime error messages.

This module is designed to handle error codes in a library or application. It supports:

1. Storing an error code internally,
2. Looking up a corresponding message string (via a user‐provided function),
3. Clearing or checking for errors.

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2. Data Structure: error_handle_t

// Presumably defined in errormanager.h:
typedef struct {
    int  error_status;                          // current error code
    void (*p_msg_lookup)(int, char*, int);      // pointer to function that fills a message buffer
} error_handle_t;

• error_status: Stores the integer code of the current error.
• p_msg_lookup: Points to a function that, given an error code, writes the corresponding message into a character buffer.

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3. Functions

3.1 new_errormanager(...)

error_handle_t* new_errormanager(void (*p_error_message)(int, char*, int))
{
    error_handle_t* error_handle;
    error_handle = (error_handle_t*)calloc(1, sizeof(error_handle_t));

    error_handle->p_msg_lookup = p_error_message;

    return error_handle;
}

• Purpose: Creates a new error_handle_t object and returns a pointer to it.
• Steps:
  1. Allocates memory (using calloc for zero-initialization).
  2. Stores the function pointer p_error_message in p_msg_lookup.
  3. Returns the pointer.

This function is effectively a constructor—it sets up an empty error manager with a callback to look up error messages.

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3.2 dst_errormanager(...)

void dst_errormanager(error_handle_t* error_handle)
{
    free(error_handle);
}

• Purpose: Frees the memory for the given error_handle_t.
• Steps:
  1. Calls free() on error_handle.
  2. No further cleanup logic is needed because there are no dynamic arrays inside error_handle_t.

Hence, it’s a simple destructor.

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3.3 set_error(...)

int set_error(error_handle_t* error_handle, int errorcode)
{
    // If the error code is 0 no action is taken and 0 is returned.
    // This is a feature not a bug.
    if (errorcode)
        error_handle->error_status = errorcode;

    return errorcode;
}

• Purpose: Stores an error code in the handle, unless it’s 0.
  • If errorcode == 0, nothing happens.
  • If nonzero, error_status is set to that code.
• Returns the errorcode (mainly for convenience).

This allows upstream code to do:

if (some_check_fail) return set_error(err_handle, SOME_ERROR_CODE);

and know the code that was set.

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3.4 check_error(...)

char* check_error(error_handle_t* error_handle)
{
    char* temp = NULL;

    if (error_handle->error_status != 0) {
        temp = (char*) calloc(ERR_MAXMSG, sizeof(char));

        if (temp)
            error_handle->p_msg_lookup(error_handle->error_status, temp, ERR_MAXMSG);
    }
    return temp;
}

• Purpose: Retrieves the message text associated with the current error_status.
• Steps:
  1. If error_status is 0, returns NULL (no error).
  2. If nonzero, allocates a temp buffer of size ERR_MAXMSG.
  3. Calls the user‐provided p_msg_lookup(error_status, temp, ERR_MAXMSG), which fills that buffer with a descriptive error string.
  4. Returns the allocated buffer pointer.

Important:

• The caller must free() the returned string if not NULL.
• This approach decouples storing the error code from the actual message creation.

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3.5 clear_error(...)

void clear_error(error_handle_t* error_handle)
{
    error_handle->error_status = 0;
}

• Purpose: Resets the stored error_status to 0 (no error).
• This is analogous to clearing the “error flag”.

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4. Typical Usage Flow

1. Create an error manager:

   error_handle_t* hErr = new_errormanager(my_lookup_func);
   

2. In various library calls:

   set_error(hErr, MY_ERR_CODE);
   

3. The caller can check if an error occurred:

   char* msg = check_error(hErr);
   if (msg != NULL) {
       fprintf(stderr, "Error: %s\n", msg);
       free(msg);
       // handle error...
   }
   

4. After handling error or if no error, optionally:

   clear_error(hErr);
   

5. When done with the library:

   dst_errormanager(hErr);
   

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5. Key Takeaways

• This code uses a function pointer (p_msg_lookup) to convert an integer error code to a text message. This design allows flexibility: the library user can supply their own message lookup mechanism.
• error_status = 0 means no error.
• ERR_MAXMSG presumably is a predefined constant (like 256 or 1024) giving the maximum error message length.
• The approach is lightweight: no complicated data structures, just a single error code plus a function pointer. It’s well‐suited for smaller C libraries that need a consistent error interface without adopting heavier frameworks.