What is the difference between main() and alt_main()?

[Altera_Forum]

I write a very simple program, driving LED through PIO. Both function can work. If using main() , the code size is 1940 bytes. If alt_main(), the code size is 472 bytes. It seems that main() include some initialization. 

 Can anyone explain the difference, or recommend some documents to read? Thanks.

[Altera_Forum]

Actually it is the default alt_main() that contains the extra code - either side of the call to main(). 

Largely this is code for initialising stdio for printf() - which pulls in a lot of library code.

[Altera_Forum]

Hi sabertooth 

 I copy here the comment to alt_main() definition  /*  * alt_main is the C entry point for the HAL. It is called by the assembler  * startup code in the processor specific crt0.S. It is responsible for:  * completing the C runtime configuration; configuring all the  * devices/filesystems/components in the system; and call the entry point for  * the users application, i.e. main().  */   Regards

[Altera_Forum]

Many thanks to Cris72.