Getting ERROR "fatal flex scanner internal error--end of buffer" missed, while handling CTRL+ C

Question

I am writing a small shell program, while trying to handle the Ctrl+C signal, I want trying to print a newline, when it is pressed.

Here's my code to do so.

static sigjmp_buf env;              

void sigint_handler(int signo){     
    siglongjmp(env, 42);            
}                                   


void myShellLoop(){                                                                  
    int parserStatus;                                                                

    signal(SIGINT, sigint_handler);                                                  

    while(1){                                                                        
        if(sigsetjmp(env,1)==42){                                                    
            printf("\n");                                                            
            continue;                                                                
        }                                                                            
        //Initialize a new command, to parse and execute.                            
        initializeGlobalCommand();                                                   

        parserStatus = yyparse();                                                    
        if(parserStatus == 0)                                                        
            executeShellCommand();                                                   
        else                                                                         
            printf("Not a valid shell command\n");                                   
    }                                                                                
}                                                                                    

But after I press Ctrl+C, it does go to a newline, but then flex gives me this error:

fatal flex scanner internal error--end of buffer missed

Here's a screenshot:

How do I handle Ctrl+C properly?

Edit: Code snippet for fork():

int execute(int cmdNumber){                                                                                                 
    pid_t pid;                                                                                                              
    int status;                                                                                                             

    pid = fork();                                                                                                           

    if(pid == 0){                                                                                                           
        signal(SIGINT, SIG_DFL);                                                                                            
        if(execvp(globalCommand.sCommands[cmdNumber].arguments[0], globalCommand.sCommands[cmdNumber].arguments) == -1){    
            perror("myShell: Command error");                                                                               
            exit(EXIT_FAILURE);                                                                                             
        }                                                                                                                   
    }                                                                                                                       
    else if(pid < 0){                                                                                                       
        //Error forking.                                                                                                    
        perror("myShell");                                                                                                  
    }                                                                                                                       
    else{                                                                                                                   
            do{                                                                                                                                                                                                                  
                waitpid(pid, &status, WUNTRACED);                                                                                                                                                                             
            }while(!WIFEXITED(status) && !WIFSIGNALED(status) && !globalCommand.background);
    }
    return 1;
}

Answer 1

you 'brutaly' go out of the (f)lex(/yacc/bison) code to come back in myShellLoop, so it is not surprising that introduces inconsistency

Redefine YY_INPUT and when control-c is hit return a special character to return a special value/token managed in your parser to call yyerror to abort in a normal way

For instance in your lexer file :

%{
...
extern void my_yy_input(char*, int *, int);

#undef YY_INPUT
#define YY_INPUT(b,r,s) my_yy_input(b,&r,s)

%}
...

with

static sigjmp_buf env;              

void sigint_handler(int signo){     
  siglongjmp(env, '@');            
}                                   

void my_yy_input( char * buff, int * nRead, int maxToRead )
{
  *nRead =  1;

  if(sigsetjmp(env,1 ) == '@') {                                                    
    *buff = '@';
    return;
  }

  *buff = getchar();
 }