Why is the compiler throwing this warning: "missing initializer"? Isn't the structure initialized?

GCC is just being overly paranoid - for no good reason in my opinion, but then it's certainly true that the GCC maintainers know a lot more about the nuances of C that I do.

See this small thread of discussion about the problem on the GCC mailing list:

• http://gcc.gnu.org/ml/gcc-bugs/1998-07/msg00031.html
• http://gcc.gnu.org/ml/gcc-bugs/1998-07/msg00059.html
• http://gcc.gnu.org/ml/gcc-bugs/1998-07/msg00128.html

Bottom line though - initializing the struct with just {0} will in fact zero initialize the whole thing.

The C99 standard says the following in 6.7.8/21 "Initialization - Sematics":

If there are fewer initializers in a brace-enclosed list than there are elements or members of an aggregate, or fewer characters in a string literal used to initialize an array of known size than there are elements in the array, the remainder of the aggregate shall be initialized implicitly the same as objects that have static storage duration.

C90 says esentially the same in 6.5.7 with a bit different wording (in other words, C99 didn't add something new here).

Also note that in C++ this was extended so that an empty set of braces, "{}", would perform value initialization on an object because there were situations (like templates) when you wouldn't even know what the members or how many members a type might have. So not only is it good practice, but necessary at times to have an initializer list that's shorter than the number of members an object might have.

This can be easily fixed for GCC in C++ programs by initializing the structure as

STARTUPINFO startupInfo = STARTUPINFO();

• just did exactly this a few days ago

You asked for as many warnings as possible using -Wall -Wextra.

In this case, you get a warning that tells you you didn't specify all fields, which is perfectly valid, but could have been unintentional.

You can suppress this warning by adding -Wno-missing-field-initializers