In the C99 Standard, 7.18.1.3 Fastest minimum-width integer types. (7.18.1.3p1) “Each of the following types designates an integer type that is usually fastest225) to operate with among all integer types that have at least the specified width.” 225) “The designated type is not guaranteed to be fastest for all purposes; if the implementation has no … Read more
I think you should use ptrdiff_t for the following reasons Indices can be negative. Therefore for a general statement, all unsigned types, including size_t, are unsuitable. The type of p2 – p1 is ptrdiff_t. If i == p2 – p1, then you should be able to get p2 back by p2 == p1 + i. … Read more
Use 3 octal digits: char problem[] = “abc\022e”; or split your string: char problem[] = “abc\x12” “e”; Why these work: Unlike hex escapes, standard defines 3 digits as maximum amount for octal escape. 6.4.4.4 Character constants … octal-escape-sequence: \ octal-digit \ octal-digit octal-digit \ octal-digit octal-digit octal-digit … hexadecimal-escape-sequence: \x hexadecimal-digit hexadecimal-escape-sequence hexadecimal-digit String literal … Read more
Unfortunately, the original ANSI C Specification specifically excludes any Preprocessor features in section 4 (“This specification describes only the C language. It makes no provision for either the library or the preprocessor.”). The C99 specification handles this explicity, though. The comments are replaced with a single space in the “translation phase”, which happens prior to … Read more
It’s actually quite common to store a number without needing to know the exact size of the type. There are plenty of quantities in my programs that I can reasonably assume won’t exceed 2 billion, or enforce that they don’t. But that doesn’t mean I need an exact 32 bit type to store them, any … Read more
The inline model in C99 is a bit different than most people think, and in particular different from the one used by C++ inline is only a hint such that the compiler doesn’t complain about doubly defined symbols. It doesn’t guarantee that a function is inlined, nor actually that a symbol is generated, if it … Read more
This is not a “static memory allocation”. Your array k is a Variable Length Array (VLA), which means that memory for this array is allocated at run time. The size will be determined by the run-time value of n. The language specification does not dictate any specific allocation mechanism, but in a typical implementation your … Read more
The behavior of type punning with union changed from C89 to C99. The behavior in C99 is the same as C11. As Wug noted in his answer, type punning is allowed in C99 / C11. An unspecified value that could be a trap is read when the union members are of different size. The footnote … Read more
TL;DR In declarations, void func1(); // obsolescent void func2(void); the behaviour is quite different. The first one declares a function without any prototype – and it may take any number of arguments! Whereas the latter declares a function with a prototype, that has no parameters and accepts no arguments. In definitions void func1() { } // … Read more
If you are on windows and using mingw, gcc uses the win32 runtime, where printf needs %I64d for a 64 bit integer. (and %I64u for an unsinged 64 bit integer) For most other platforms you’d use %lld for printing a long long. (and %llu if it’s unsigned). This is standarized in C99. gcc doesn’t come … Read more