Tag: #semantics

extern declares a variable without defining it, allowing the linker to find the definition elsewhere. This is useful when a variable is declared in one file but defined in another. 2017-08-27

Integers in C are int by default, while suffixes like L and U denote long and unsigned types. Floats are double without a suffix. 2017-01-23

Literals are lvalues with addresses, while constants are rvalues without addresses. In C, only string literals are literals; other “literals” like numbers and characters are constants. 2017-01-22

“lvalue” either means “expression which can be placed on the left-hand side of the assignment operator”, or means “expression which has a memory address”. “rvalue” is defined as “all other expressions”. 2017-01-21

A union in C allows one variable to hold different data types, where the storage is shared. The size of a union is at least the size of its largest member. Fields in a union have the same byte offset. 2017-01-03

GCC’s ‘statement expressions’ allow inserting statements into expression positions. Behavior is unspecified. 2016-12-30

C allows a single array field of incomplete type (char []) at the end of a struct definition. The size of the struct is determined by the size of the fixed fields, and the dynamic-sized array is allocated separately. 2016-12-27

C array literals can use explicit indexes. The array length is determined by the largest explicit index. 2016-12-25

static functions in C are only callable within the translation unit they are defined in, not across the whole program. 2016-12-12

Arrays in C can “decay” to pointers, but are not inherently pointers. The size of an array is lost during decay. 2016-12-08

The restrict keyword in C is a type qualifier that indicates a pointer parameter points to an object not accessed through any other pointer in the function’s scope. This allows the compiler to make optimizations. 2016-12-03

const is a type qualifier in C that makes a variable unassignable, except during initialization. 2016-12-02

Computing a pointer to unowned memory invokes undefined behavior, even without dereferencing! 2016-11-30

void in a C function parameter list means the function takes no arguments, whereas an empty list allows for an unspecified number of arguments. 2016-11-27

void in C has multiple meanings: as a return type to indicate no return value, as a parameter type to indicate no parameters, and as a pointer type to indicate a pointer to an unknown type. 2016-11-27