c++ - Why is the double pound needed in one place but not the others in this macro? -


in particular bit of code, author clever using macro create incrementor functions members of class counter.

class counter {     public:         uint64 _call;         uint64 _call_indirect;         uint64 _return;         uint64 _syscall;         uint64 _branch;         uint64 _branch_indirect;          counter() : _call(0),_call_indirect(0), _return(0), _branch(0), _branch_indirect(0) {}          uint64 total()         {              return _call + _call_indirect + _return + _syscall + _branch + _branch_indirect;         } };  counter countseen; counter counttaken;  #define inc(what) void inc ## (int32 taken) { countseen. ++; if( taken) counttaken. ++;}  inc(_call) inc(_call_indirect) inc(_branch) inc(_branch_indirect) inc(_syscall) inc(_return)

i'm little confused macro, though. why author use double pound in function definition part of macro , not when being used class variable being incremented?

edit: double pound concatenation, confusion comes why double pound not necessary in "countseen. ++" , "counttaken. ++" parts.

let’s @ first macro (inc(_call)) call expands to:

void inc_call (int32 taken) { countseen. _call ++; if( taken) counttaken. _call ++;}

reformatting bit, get:

void inc_call (int32 taken) {     countseen._call++;     if(taken)         counttaken._call++; }

this declares function, inc_call, increments countseen._call , maybe counttaken._call. since variables aren’t called ._call (which invalid token, since can’t start name period), period should not glued macro argument. similarly, since _call++ isn’t valid token (it’s 2 tokens; can’t include plus signs in name), there shouldn’t pound signs there.

however, without first ##, result start void inc _call (int32 taken), invalid c++ because have 2 function names.


Comments

Post a Comment

Popular posts from this blog

php - Vagrant up error - Uncaught Reflection Exception: Class DOMDocument does not exist -

i've set bento/ubuntu-16.04 vagrant box using php 5.6, , getting following error quite few times when try , run shell script: "uncaught reflection exception: class domdocument not exist". i've tried adding following top of script (not together), each no success: "sudo apt-get install php5.6-xml", "sudo apt-get install php5-xml", "sudo apt-get install php-dom" i've tried resetting server "sudo service apache2 restart". does have suggestions?
Read more

vue.js - Create hooks for automated testing -

Image
qa guys complained can't automate frontend testing. because our html looks same outside. lazy hack did this <template> <div :role="$options.name"> ... </div> </template> <script> export default { name: 'vmcomponentname' } </script> which takes name script , applies html. in browser get: <div role="vmcomponentname"> ... </div> line :role="$options.name" goes in every component. is there dry er solutions? please share. additional details i'll explain in details looking for. imagine have vmusercreate form creates user. test case can create user . to automatically test without role, have use following selector: .wrapper > .wrapper > .wrapper > .submit-button the test extremely brittle (will break lot). if use roles can use [role="vmusercreateform"] .submit-button selector. many folds less brittle. so basically, i'm ...
Read more

Add new key value to json node in java -

i have json file : { "id":1, "name":"abc", "addressdetails": { "city":"newyork" } } i wanted add 1 more key-value ("pincode" : "414141") node 'addressdetails'. i tried using : objectmapper mapper = new objectmapper(); jsonnode root = mapper.readtree(new file("d://test.json")); objectnode node = mapper.createobjectnode(); node.with("addressdetails").put("pincode", "414141"); but it's not getting added, there way can ? you can try you should modify file path objectmapper mapper = new objectmapper(); objectnode nodes = mapper.readvalue(new file("d:\\test.txt"), objectnode.class); nodes.with("addressdetails").put("pincode", "414141"); mapper.writer().writevalue(new file("d:\\test.txt"), nodes);
Read more