The MDM string parser uses the Line_type to determine how to interpret each line. A command list begins with the MCI_COMMAND_HEAD Line_type and ends with the MCI_END_COMMAND Line_type.

MCI_RETURN

This Line_type indicates that the command provides return information. If used, MCI_RETURN must be the second entry in the command list.

• Column 1 contains "".
  
• Column 2 contains the type of return: integer or string.
  
• Column 3 contains MCI_RETURN.
A command returning an integer requires a ULONG for that return value. A command returning a string requires two ULONGs: the first ULONG is for a pointer to the return buffer, and the second ULONG is for the return buffer size.

The parser sends back return information in the pszReturnString and usReturnLength parameters of the mciSendString function. The above example shows how both types of returns are used.

The MCI_OPEN returns a ULONG value, and MCI_INFO returns data that is filled into the buffer pointed to by the pointer in the second ULONG of the command structure. (Remember that the first ULONG is always hwndCallback.)

MCI_RETURN_TYPE
This Line_type is used to convert return values into strings by the string parser.

   "",              MCI_TRUE_FALSE_RETURN, 0,    MCI_RETURN_TYPE,
      "TRUE",       1L,                          MCI_RETURN_TYPE_STRING,
      "FALSE",      0L,                          MCI_RETURN_TYPE_STRING,
   "",              0L,                          MCI_END_RETURN_TYPE,

The flag_define field for the return line is compared against the high-order word of the return code. If a match is found, then the parser tries to find a match for the flag_define field and the return value. If a match is found for the return value, then the keyword string is returned to the application in the pszReturnString field of the mciSendString call.

MCI_FLAG
This Line_type is used to convert keywords to flag values for ulParam1. When more than one MCI_FLAG Line_type is encountered during the parsing of a command string, the ulParam1 parameter is ORed with the flag_define field of the Keyword_list.
MCI_STRING
This Line_type is used for string values for a message. The string following the MCI_STRING keyword is copied into the command structure. MDM allocates memory to hold the string and put the address into the command structure.
MCI_INTEGER
This Line_type is used for integer values for a message. The integer following the MCI_INTEGER keyword is copied into the command structure. The integer value is converted from a string representation to a ULONG.
MCI_CONSTANT
This Line_type and the MCI_END_CONSTANT Line_type allow a set of possible keywords to represent a flag or integer. In the following example, any one of the time format values can be used as the value for the time format constant.

  "",                            MCI_SET_TIME_FORMAT,     MCI_CONSTANT,
     "time format milliseconds", MCI_FORMAT_MILLISECONDS, MCI_INTEGER,
     "time format ms",           MCI_FORMAT_MILLISECONDS, MCI_INTEGER,
     "time format mmtime",       MCI_FORMAT_MMTIME,       MCI_INTEGER,
  "",                            0L,                      MCI_END_CONSTANT,

The value on the MCI_CONSTANT line_type is ORed with the ulParam1 field. The values on the MCI_INTEGER line_types within this constant block are copied into the command structure. The constant block represents just one ULONG in the command structure.

MCI_DEFAULT_STRING
This Line_type and the MCI_DEFAULT_INTEGER Line_type provide the means for an unknown value to be used as a string or integer. For example the LOAD command (shown in the following example) uses a default string for the filename string.

"load",                          MCI_LOAD, 0,           MCI_COMMAND_HEAD,
   "notify",                     MCI_NOTIFY,            MCI_FLAG,
   "wait",                       MCI_WAIT,              MCI_FLAG,
   "new",                        0L,                    MCI_FLAG,
   "readonly",                   MCI_READONLY,          MCI_FLAG,
   "",                           MCI_OPEN_ELEMENT,      MCI_DEFAULT_STRING,
"",                              0L,                    MCI_END_COMMAND,

MCI_RECTL
This Line_type specifies that RECTL data modifies the media control interface flag represented by the command list entry. The second column of this entry contains the flag to set. The data structure for the message command must reserve a ULONG to hold the integer value.
MCI_OR
This Line_type allows you to combine different line types within the same construct. The following shows an example of an MCI_OR entry used in the MCI_STATUS command list in the MDMCMD.RC file. Notice that the %d symbol can be used in a command list as an indicator to print the decimal value.

   "",              0L,                         MCI_OR,
   "track",         MCI_TRACK,                  MCI_INTEGER,
   "channel",       0L,                         MCI_CONSTANT,
      "all",        MCI_STATUS_AUDIO_ALL,       MCI_INTEGER,
      "left",       MCI_STATUS_AUDIO_LEFT,      MCI_INTEGER,
      "right",      MCI_STATUS_AUDIO_RIGHT,     MCI_INTEGER,
      "%d",         0L,                         MCI_INTEGER,
   "",              0L,                         MCI_END_CONSTANT,
   "",              0L,                         MCI_END_OR,

MCI_STRING_LIST
Pointer to an array of pointers to strings in the list. For example, the following example code uses MCI_STRING_LIST to point to an array of pointers to device identifiers.

"group",            MCI_GROUP, 0,               MCI_COMMAND_HEAD,
   "delete",        MCI_GROUP_DELETE,           MCI_FLAG,
   "nopiecemeal",   MCI_NOPIECEMEAL,            MCI_FLAG,
   "synchronize",   MCI_SYNCHRONIZE,            MCI_FLAG,
   "wait",          MCI_WAIT,                   MCI_FLAG,
   "notify",        MCI_NOTIFY,                 MCI_FLAG,
   "",              0L,                         MCI_INTEGER,
   "",              0L,                         MCI_INTEGER,
   "master",        MCI_GROUP_MASTER,           MCI_STRING,
   "",              0L,                         MCI_STRING,
   "",              0L,                         MCI_INTEGER,
   "make",          MCI_GROUP_MAKE,             MCI_STRING_LIST,
"",                 0L,                         MCI_END_COMMAND,

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