Wiki MarkupSection 6.5.2.5 of the ISO/IEC 9899:1999 (C99) standard defines a compound literal as \[ [ISO/IEC 9899:1999|AA. Bibliography#ISO/IEC 9899-1999]\]

A postfix expression that consists of a parenthesized type name followed by a brace-enclosed list of initializers ... The value of a compound literal is that of an unnamed object initiated by the initializer list

Wiki MarkupThe storage for this object is either static (if the compound literal occurs at file scope) or automatic (if the compound literal occurs at block scope), and the storage duration is associated with its immediate enclosing block (\[[ISO/IEC 9899:1999|AA. Bibliography#ISO/IEC 9899-1999]\], Section 6.5.2.5.6).

For example, in the function

void func(void) {
  int *ip = (int[4]){1,2,3,4};
  /* ... */
}

Wiki Markupfollowing initialization, the {{int}} pointer {{ip}} contains the address of an unnamed object of type {{int \ [4\]}}, allocated on the stack. Once {{func}} returns, any attempts to access this object will produce undefined behavior.unmigrated-wiki-markup

Note that only one object is created per compound literal \ -\- even if the compound literal appears in a loop and has dynamic initializers (\[[ISO/IEC 9899:1999|AA. Bibliography#ISO/IEC 9899-1999]\], Section 6.5.2.5.16).

This recommendation is a specific instance of rule DCL30-C. Declare objects with appropriate storage durations.

Noncompliant Code Example

Wiki MarkupIn this noncompliant code example, the programmer mistakenly assumes that the elements of the {{ints}} array of the pointer to {{int_struct}} are assigned the addresses of distinct {{int_struct}} objects, one for each integer in the range \ [0, MAX_INTS-1\]:

#include <stdio.h>

typedef struct int_struct {
  int x;
} int_struct;

#define MAX_INTS 10

int main(void){
  size_t i;
  int_struct *ints[MAX_INTS];

  for (i = 0; i < MAX_INTS; i++) {
    ints[i] = &(int_struct){i};
  }

  for (i = 0; i < MAX_INTS; i++) {
    printf("%d\n", ints[i]->x);
  }
}

...