Appendix C -Xs Differences Between Sun C and ANSI/ISO C

Aggregate initialization: 

struct

{ 

int a[3];

int b; 

} 

w[] = {{1},2};

sizeof (w) = 16 w[0].a = 1, 0, 0 w[0].b =2

sizeof(w) = 32 w[0].a = 1, 0, 0 w[0].b = 0 w[1].a = 2, 0, 0 w[1].b = 0

Incomplete struct, union, enum declaration

struct fq { int i; struct unknown; };

Does not allow incomplete struct, union, and enum declaration.

Switch expression integral type 

Allows non-integral type. 

Does not allow non-integral type. 

Order of precedence 

Allows: 

if (rcount > count += index)

Does not allow: 

if (rcount > count += index)

unsigned, short, and long typedef declarations

Allows: 

typedef short small unsigned small;

Does not allow (all modes). 

struct or union tag mismatch in nested struct or union declarations

Allows tag mismatch: 

struct x  

{ int i; } s1; /* K&R treats as a struct */ { union x s2; }

Does not allow tag mismatch in nested struct or union declaration.

Incomplete struct or union type

Ignores an incomplete type declaration. 

struct x  

{ int i; }

s1; main() { struct x; struct y {struct x f1

/* in K&R, f1 refers */ /* to outer struct */ } s2; struct x { int i;

};

}

Casts as lvalues

Allows: 

(char *) ip = &foo;

Does not allow casts as lvalues (all modes).