5.69 Flexible array members in C99

In a struct with more than one member, the last member of the struct can have incomplete array type. Such a member is called a flexible array member of the struct.


When a struct has a flexible array member, the entire struct itself has incomplete type.

Flexible array members enable you to mimic dynamic type specification in C in the sense that you can defer the specification of the array size to runtime. For example:

extern const int n;
typedef struct
    int len;
    char p[];
} str;
void foo(void)
    size_t str_size = sizeof(str);  // equivalent to offsetoff(str, p)
    str *s = malloc(str_size + (sizeof(char) * n));
Related concepts
5.63 New language features of C99
5.65 // comments in C99 and C90
5.66 Compound literals in C99
5.67 Designated initializers in C99
5.68 Hexadecimal floating-point numbers in C99
5.70 __func__ predefined identifier in C99
5.71 inline functions in C99
5.72 long long data type in C99 and C90
5.73 Macros with a variable number of arguments in C99
5.74 Mixed declarations and statements in C99
5.75 New block scopes for selection and iteration statements in C99
5.76 _Pragma preprocessing operator in C99
5.77 Restricted pointers in C99
5.79 Complex numbers in C99
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