sprintf or snprintf does not work in SLDRT kernel mode
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I was using the following code which uses snprintf() to create a GPS message within a S-function builder and it worked well in the connected I/O mode. But, when I tried to run the same code in kernel mode, the output becomes all 0s. I was wondering if there is a workaround or another similar function that I can use to get the same result in the kernel mode.
I tried both MINGW 6.3 and Visual C++ 2017 compilers.
// Packing the data
(void)snprintf(temp_packet, sizeof temp_packet, "$GPGGA," // Message ID
"%02d%02d%06.3f," // UTC_Time
"%02d%08.5f," // Latitude
"%1c," // N/S Indicator
"%03d%08.5f," // Longitude
"%1c," // E/W Indicator
"%1u," // Position Fix Indicator
"%02u," // Satellites used
"%.2f," // HDOP
"%.1f," // MSL Altitude
"M," // M, meters
"," // Geoid Separation, not used
"M," // M, meters
"," // Age of Differential Corrections, not used
"%u" // Diff Reference Station ID
"*" // Start of a checksum
,(int)time_hh, (int)time_mm, time_ss, // UTC_Time
(int)lat_dd, lat_mm, // Latitude
lat_ns, // N/S Indicator
(int)lon_ddd, lon_mm, // Longitude
lon_ew, // E/W Indicator
*Position_Fix, // Position Fix Indicator
*Satellites, // Satellites used
*HDOP, // HDOP
*MSL_Altitude_m, // MSL Altitude
// Age of Differential Corrections, not used
*Diff_Station_ID // Diff Reference Station ID
// Start of a checksum
Jan Houska on 18 May 2023
I'm not sure what is exactly your use case, but if you are using snprintf to form a message you will then send to some device e.g. over UDP, you may want to consider the Stream Output block. This block accepts numeric inputs and formats them according to a C-like format string to create text message. Using this block is typically much easier than writing a S-function that does the same. The block also provides other benefits, like automatic data type conversion, and such.
That said, snprintf (which should be always used instead of sprintf) should work and it is in fact internally used by the Stream Output block. I don't quite understand what do you mean by "all zeros" - does this mean the numbers are correctly formatted, but zeros? Like e.g. 00.00000 for latitude? Could you please try literal constants instead of the variables, like e.g. 19.23456 instead of lat_mm ? Do these also come out as zeros? You can also try to shorten the format string to just one or two values - is the problem still there?
And, a final remark - Simulink Desktop Real-Time always uses its own built-in compiler (Clang), so it is not relevant which compiler you use to build your S-function.