{"id":6073,"date":"2006-10-20T13:22:00","date_gmt":"2006-10-20T13:22:00","guid":{"rendered":"https:\/\/blogs.msdn.microsoft.com\/vcblog\/2006\/10\/20\/crt-initialization\/"},"modified":"2019-02-18T18:54:40","modified_gmt":"2019-02-18T18:54:40","slug":"crt-initialization","status":"publish","type":"post","link":"https:\/\/devblogs.microsoft.com\/cppblog\/crt-initialization\/","title":{"rendered":"CRT Initialization"},"content":{"rendered":"

Hi, I’m George Mileka and I work on the Visual C++ libraries team. My team owns the CRT, ATL, MFC and STL…<\/p>\n

One subject I have always been interested in is the startup code and initialization. The subject got even more challenging as we started supporting mixing native and managed code in our binaries.<\/p>\n

Today I will talk about how the CRT initializes global states in the native world… <\/p>\n

By default, the linker includes the CRT library which provides its own startup code. The CRT startup code initializes the CRT library, calls global initializers, and finally calls user-provided “main()” function (for console applications).<\/p>\n

Now, consider the following code:<\/p>\n

          int func(void)<\/p>\n

          {<\/p>\n

                        return 3;<\/p>\n

          }<\/p>\n

          int gi = func();
 
          int main()<\/p>\n

          {<\/p>\n

                        return gi;<\/p>\n

          }<\/p>\n

According to the C\/C++ standard, func() must be called before main() is executed. But who calls it?<\/p>\n

An easy way to know, is to set a breakpoint in func(), start debugging the application and look at the stack! Luckily, the CRT code ships with VS!<\/p>\n

Browsing the functions on the stack, you will find that the CRT is simply looping through a list of function pointers, calling each one as it goes through them. Those functions are either ones like func() or constructors for class instances…<\/p>\n

So, where does the CRT get that list from?<\/p>\n

There is a contract between the CRT and VC++ Compiler:<\/p>\n