lex＆yacc多定义错误

Question

I want to make code scanner and parser but I don't know why this error happens just by looking at the error log. The scanner takes the sample code and divides it into tokens, then returns what each of the tokens in the code is doing.The parser receives the values returned from the scanner and parses the code according to the rules. It checks validity of grammar of sample code.

and finally this my error

lex.yy.o: In function main:
lex.yy.c:(.text+0x1d2a): multiple definition of main
y.tab.o:y.tab.c:(.text+0x861): first defined here
collect2: error: ld returned 1 exit status

Answer 1

You have defined main in both your files, but C only allows a single definition of main in a program, which is what the linker error is telling you.

The main in your scanner file has an invalid prototype (C hasn't allowed function definitions without a return type for almost 20 years) and also calls yylex only once, which is not going to do much. So it seems pretty well pointless. If you want to debug your scanner without using the parser,byou can link the scanner with -lfl ; that library includes a definition of main which repeatedly calls yylex until end of file is signalled.

Instead of scattering printf calls through your scanner, you can just build a debugging version of the scanner using the --debug flag when you generate the scanner. That will print out a trace of all scanner actions.