Results-reproducibility.md

@@ -18,6 +18,7 @@ test_input.txt             # input file used for calculations
 test_predefines.h          # predefines selected at compilation stage
 test_problem-definition.h  # user's definition of the problem 
 test_logger.h              # user's logger
+test.stdout                # standard output generated by the code
 ```
 This provides full information (apart from any external data added by user) required to reproduce your results.
 
@@ -29,7 +30,15 @@ This provides full information (apart from any external data added by user) requ
 ```bash
 scp outprefix* new_location
 ``` 
+5. When printing messages to `stdout` use functions:
+```c
+// prints to stdout and to file outprefix.stdout
+void wprintf( const char * format, ... );       
 
+// prints to stream (like stdout or stderr) and to file outprefix.stdout         
+void wfprintf(FILE *stream,  const char * format, ... );
+```
+These are analogs of [printf](http://www.cplusplus.com/reference/cstdio/printf/) and [fprintf](http://www.cplusplus.com/reference/cstdio/fprintf/) with the difference that the message will added also to `outprefix.stdout`.  
 
 To learn more about good practices related to results reproducibility issue see:
 * [Creating Reproducible Data Science Projects](https://towardsdatascience.com/creating-reproducible-data-science-projects-1fa446369386)
\ No newline at end of file