{"id":5553,"date":"2007-08-03T16:28:00","date_gmt":"2007-08-03T16:28:00","guid":{"rendered":"https:\/\/blogs.msdn.microsoft.com\/vcblog\/2007\/08\/03\/testing-compiler-diagnostics-and-a-cool-ide-tip\/"},"modified":"2019-02-18T18:54:24","modified_gmt":"2019-02-18T18:54:24","slug":"testing-compiler-diagnostics-and-a-cool-ide-tip","status":"publish","type":"post","link":"https:\/\/devblogs.microsoft.com\/cppblog\/testing-compiler-diagnostics-and-a-cool-ide-tip\/","title":{"rendered":"Testing Compiler Diagnostics…and a Cool IDE Tip!"},"content":{"rendered":"

Hello everyone, this is Jamie Eckman.  <\/span>The last time I posted I was an SDET (tester) on the Libraries team.  <\/span>I’ve since moved to the Compiler team, still as an SDET.  <\/span>One thing we see a lot of on both teams is compiler diagnostics: warnings and errors.<\/font><\/p>\n

One of our Libraries developers, Stephan T. Lavavej, wrote this last year on one of our internal discussion lists: Figuring out the mapping from “what the compiler is complaining about” to “what’s actually wrong with my code, if anything” is like 75% of learning how to program. <\/em><\/span>Depending on how you learned to program, 75% may or may not be an overstatement, but the point is clear.  <\/span>Everyone writes bad code sooner or later, and in the case of new programmers it’s sooner (and often).  <\/span>For this reason it’s important that the errors the compiler emits are correct and clear enough to diagnose the problem.  <\/span>Clarity is something we’re making a significant investment into improving over the next few releases of Visual Studio.  <\/span>For now I’ll mostly stick to talking about correctness.<\/span><\/span><\/font><\/font><\/p>\n

When I was still on the Libraries team the only direct contact with diagnostics I had was some maintenance of the ATL Server attributes error tests.  <\/span>But for the most part I looked at compiler errors from the end-user perspective:  <\/span>This test I wrote doesn’t compile, why?  <\/span>Now that I’m on the Compiler team, which owns the bulk of the error text you’re likely to see while writing C or C++ code, I’ve had a great opportunity to look at up close how our diagnostics work and how we test them.<\/font><\/p>\n

The compiler has on the order of 1,000 errors and warnings it can emit.  <\/span>We test these like you might expect, each warning or error has one or more test cases associated with it.  <\/span>The test cases verify that the diagnostic that’s expected is actually emitted and is emitted on the correct line.  <\/span>Of course, the compiler is a hugely complex mechanism and problems are bound to slip through the cracks.<\/font><\/p>\n

A colleague on our UE team (User Education, responsible for the content on MSDN, among other things) recently came to me with a small list of code snippets from the <\/font>C\/C++ Build Errors<\/font><\/a> section of MSDN that weren’t producing the promised errors.  <\/span>These snippets are pretty useful when you’re trying to figure out what a particular error or warning means.  <\/span>Oftentimes the simplified code in the snippet can help you spot the problem in your own code.<\/font><\/p>\n

So, Tim from the UE team asked me to look at these snippets that weren’t working and figure out what was wrong.  <\/span>A compiler bug, an expected change we forgot to tell UE about, or something else?  <\/span>As an example, here’s the first one I looked at:<\/font><\/p>\n

\/\/ C2062_b.cpp<\/p>\n

<\/span><\/p>\n

\/\/ compile with: \/c<\/p>\n

<\/span><\/p>\n

class<\/span> DataSent {};<\/p>\n

<\/span><\/p>\n

<\/p>\n

 <\/p>\n

<\/span><\/p>\n

struct<\/span> MyDataController {<\/p>\n

<\/span><\/p>\n

   <\/span>MyDataController(int<\/span> age, DataSet* j) {}   <\/span>\/\/ C2062<\/p>\n

<\/span><\/span><\/p>\n

   <\/span>\/\/ try the following line instead<\/p>\n

<\/span><\/span><\/p>\n

   <\/span>\/\/ MyDataController(int age, DataSent* j) {}<\/p>\n

<\/span><\/span><\/p>\n

};<\/span><\/p>\n

This is a simple error, although perhaps not easy to spot.  <\/span>The class name “DataSent” has been mistyped “DataSet”.  <\/span>The expected error is C2062, “type ‘DataSet’ unexpected”.  <\/span>The error that actually gets emitted (with a recent Orcas compiler) is C2061, “syntax error : identifier ‘DataSet’”.  <\/span>Here we see that correctness and clarity often have an interesting relationship when it comes to error messages.  <\/span>Although we didn’t get the error we expected, the error we did get nonetheless points us directly at the problem.  <\/span>I might be able to make the case that this is a compiler bug, but because the new error is functionally just as good as the old error, it’s unlikely to be fixed at this stage in the Orcas release cycle.<\/font><\/p>\n

Now, here’s a tip that has abso\nlutely nothing to do with the rest of this post.  <\/span>Some of you may already know this, but I haven’t seen it posted on vcblog yet.  <\/span>I recently started working in a new codebase with a pretty strict set of coding conventions.  <\/span>One of the conventions is that nothing should go past column 79.  <\/span>It’s pretty annoying to watch the column display in the status bar every time you get close to the end of a line, but fortunately there’s a nifty hidden feature of Visual Studio that can help.  <\/span>Column guides.  <\/span>This involves editing the registry, so the standard disclaimer applies: Modify the registry at your own risk!<\/font><\/p>\n

Find this key in your registry:<\/font><\/p>\n

HKEY_CURRENT_USERSoftwareMicrosoftVisualStudio9.0Text Editor<\/font><\/p>\n

For Visual Studio 2005 you’ll want to use “8.0” instead of “9.0”.  <\/span>Create a new String Value in the Text Editor key and call it “Guides”.  <\/span>Modify the data for Guides and add something like this:<\/font><\/p>\n

RGB(0, 128, 0) 79<\/font><\/p>\n

This will put a green line at column 79.  <\/span>You can have multiple guides:<\/font><\/p>\n

RGB(0, 128, 0) 79, RGB(128, 0, 0) 49<\/font><\/p>\n

Make sure you restart Visual Studio after you add these values for the changes to take effect.<\/font><\/p>\n

Enjoy!<\/font><\/p>\n

– Jamie<\/font><\/p><\/p>\n","protected":false},"excerpt":{"rendered":"

Hello everyone, this is Jamie Eckman.  The last time I posted I was an SDET (tester) on the Libraries team.  I’ve since moved to the Compiler team, still as an SDET.  One thing we see a lot of on both teams is compiler diagnostics: warnings and errors. One of our Libraries developers, Stephan T. Lavavej, […]<\/p>\n","protected":false},"author":289,"featured_media":35994,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[1],"tags":[11],"class_list":["post-5553","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-cplusplus","tag-test"],"acf":[],"blog_post_summary":"

Hello everyone, this is Jamie Eckman.  The last time I posted I was an SDET (tester) on the Libraries team.  I’ve since moved to the Compiler team, still as an SDET.  One thing we see a lot of on both teams is compiler diagnostics: warnings and errors. One of our Libraries developers, Stephan T. Lavavej, […]<\/p>\n","_links":{"self":[{"href":"https:\/\/devblogs.microsoft.com\/cppblog\/wp-json\/wp\/v2\/posts\/5553","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/devblogs.microsoft.com\/cppblog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/devblogs.microsoft.com\/cppblog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/cppblog\/wp-json\/wp\/v2\/users\/289"}],"replies":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/cppblog\/wp-json\/wp\/v2\/comments?post=5553"}],"version-history":[{"count":0,"href":"https:\/\/devblogs.microsoft.com\/cppblog\/wp-json\/wp\/v2\/posts\/5553\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/cppblog\/wp-json\/wp\/v2\/media\/35994"}],"wp:attachment":[{"href":"https:\/\/devblogs.microsoft.com\/cppblog\/wp-json\/wp\/v2\/media?parent=5553"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/cppblog\/wp-json\/wp\/v2\/categories?post=5553"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/cppblog\/wp-json\/wp\/v2\/tags?post=5553"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}