A four-character code is a 32-bit quantity representing a sequence of one to four ASCII alphanumeric characters, padded on the right with blank characters. The data type for a four-character code is FOURCC. Use the mmioFOURCC function to convert four characters to a four-character code, as shown in the following code fragment, which generates a four-character code for “WAVE”:
FOURCC fourccID;
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fourccID = mmioFOURCC('W', 'A', 'V', 'E');
To convert a null-terminated string into a four-character code, use mmioStringToFOURCC, as shown in the following code fragment, which also generates a four-character code for “WAVE”:
FOURCC fourccID;
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fourccID = mmioStringToFOURCC("WAVE", 0);
The second parameter in mmioStringToFOURCC specifies options for converting the string to a four-character code. If you specify the MMIO_TOUPPER flag, mmioStringToFOURCC converts all alphabetic characters in the string to uppercase. This is useful when you need to specify a four-character code to identify a custom I/O procedure (four-character codes identifying file-extension names must be all uppercase).