C program to read excel file

Try this: DispHelper[^]

Put a value into column 4 row 10:

dhPutValue(xlSheet, L".Cells(%d,%d) = %s", 10, 4, szCellText);

Excel exposes a COM API, so you could use that from C. But unelss your COM skills are exceptionally good, it will be a very difficult task. It would be far easier to do this from C++ or even C# (via interop).

[Edit]
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Guess what? Turns out Excel has a C API (no need to go the COM route).

See http://msdn.microsoft.com/en-us/library/bb687829.aspx[^]

[Edit 2]
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A quick read indicates that maybe it's more for writing faster functions, so it's probably not stand-alone. So while you can use that, you'd probably still need to use COM.