SIMPOL Documentation

In the previous section we discussed in-depth a program in SBL that calls a SIMPOL function in a library called jpeglib.sml. The actual function in the SIMPOL source code needs to be written to the interface provided by SMEXEC. In this section we will look at that function.

The original function prototype in SIMPOL is as follows:

Unfortunately this function cannot be called via SMEXEC directly, since functions that are called from SMEXEC, as we learned in the previous section, can only take a single string argument and can only return a string result. That means that we will have to create an interface function that can be called via SMEXEC and that can then call the desired function and return the results in the correct format. For ease of understanding later, we can call this function smexec_getjpegsize(). The source code for the interface function is shown below:

function smexec_getjpegsize(string sFilename) export
  string sResult
  integer iWidth, iHeight, iResult

  iWidth = 0
  iHeight = 0
  iResult = getjpegsize(sFilename, iWidth, iHeight)
  if iResult == 0
    sResult = "w:" + .tostr(iWidth, 10) + " h:" + \
              .tostr(iHeight, 10)
  else
    sResult = "e:" + .tostr(iResult, 10)
  end if
end function sResult

In the interface function the only parameter passed in is the sFilename parameter and the values of the two integers are converted to strings and passed in the return value if the function succeeds and if it fails the error value is passed in the return value. The programmer is free here to implement any method desired to transmit the information via the string result back to the caller.