/in/foo.cc: In function 'char io::gc()':
/in/foo.cc:7:63: warning: operation on 'io::p1' may be undefined [-Wsequence-point]
  inline char gc(){if(p1!=p2){return *p1++;} return p1==(p2=(p1=buf)+fread(buf,1,1<<21,stdin))?EOF:*p1++;}
                                                            ~~~^~~~~