2.9BSD/usr/src/cmd/lex/lib/allprint.c

# include <stdio.h>
allprint(c)
  char c; {
        extern FILE *yyout;
        switch(c){
                case '\n':
                        fprintf(yyout,"\\n");
                        break;
                case '\t':
                        fprintf(yyout,"\\t");
                        break;
                case '\b':
                        fprintf(yyout,"\\b");
                        break;
                case ' ':
                        fprintf(yyout,"\\\bb");
                        break;
                default:
                        if(!printable(c))
                                fprintf(yyout,"\\%-3o",c);
                        else 
                                putc(c,yyout);
                        break;
                }
        return;
        }
sprint(s)
  char *s; {
        while(*s)
                allprint(*s++);
        return;
        }
printable(c)
  int c;
        {
        return(040 < c && c < 0177);
        }