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The order of evaluation of subexpressions, including
+, -, =, * , /), with the exception of:
&& and ||), ?:), and ,)is Unspecified
For example
int Hello()
{
return printf("Hello"); /* printf() returns the number of
characters successfully printed by it
*/
}
int World()
{
return printf("World !");
}
int main()
{
int a = Hello() + World(); //might print Hello World! or World! Hello
/** ^
|
Functions can be called in either order
**/
return 0;
}
sdcc 29.7/ucSim/Z80
We like to think that:
..09a minus shifts backwards
but '(t=-1,(15<<t)==7)' is false.
..19-2 short<int
but 'sizeof(short)<sizeof(int)' is false.
..22 floating point is always IEEE
but 'STDC_IEC_559_is_defined' is false.
..25 pointer arithmetic works outside arrays
but '(diff=&var.int2-&var.int1, &var.int1+diff==&var.int2)' is false.
From what I can say with my puny test cases, you are Stop at 0x0013f3: (106) Invalid instruction 0x00dd
printf crashes. "O_O"
gcc 4.4@x86_64-suse-linux
We like to think that:
..05 int has the size of pointers
but 'sizeof(int)==sizeof(void*)' is false.
..08 overshifting is okay
but '(1<<bits_per_int)==0' is false.
..09a minus shifts backwards
but '(t=-1,(15<<t)==7)' is false.
..14 i++ is strictly left to right
but '(i=0,a[i++]=i,a[0]==1)' is false.
..15 structs are packed
but 'sizeof(char_int)==(sizeof(char)+sizeof(int))' is false.
..17 size_t is unsigned int
but 'sizeof(size_t)==sizeof(unsigned int)' is false.
..26 sizeof() does not evaluate its arguments
but '(i=10,sizeof(char[((i=20),10)]),i==10)' is false.
From what I can say with my puny test cases, you are 79% mainstream
gcc 4.4@x86_64-suse-linux(-O2)
We like to think that:
..05 int has the size of pointers
but 'sizeof(int)==sizeof(void*)' is false.
..08 overshifting is okay
but '(1<<bits_per_int)==0' is false.
..14 i++ is strictly left to right
but '(i=0,a[i++]=i,a[0]==1)' is false.
..15 structs are packed
but 'sizeof(char_int)==(sizeof(char)+sizeof(int))' is false.
..17 size_t is unsigned int
but 'sizeof(size_t)==sizeof(unsigned int)' is false.
..26 sizeof() does not evaluate its arguments
but '(i=10,sizeof(char[((i=20),10)]),i==10)' is false.
From what I can say with my puny test cases, you are 82% mainstream
clang 2.7@x86_64-suse-linux
We like to think that:
..05 int has the size of pointers
but 'sizeof(int)==sizeof(void*)' is false.
..08 overshifting is okay
but '(1<<bits_per_int)==0' is false.
..09a minus shifts backwards
but '(t=-1,(15<<t)==7)' is false.
..14 i++ is strictly left to right
but '(i=0,a[i++]=i,a[0]==1)' is false.
..15 structs are packed
but 'sizeof(char_int)==(sizeof(char)+sizeof(int))' is false.
..17 size_t is unsigned int
but 'sizeof(size_t)==sizeof(unsigned int)' is false.
..21a Function Arguments are evaluated right to left
but '(gobble_args(0,ltr_fun(1),ltr_fun(2),ltr_fun(3),ltr_fun(4)),ltr_result==4321)' is false.
ltr_result is 1234 in this case
..25a pointer arithmetic works outside arrays
but '(diff=&p1-&p2, &p2+diff==&p1)' is false.
..26 sizeof() does not evaluate its arguments
but '(i=10,sizeof(char[((i=20),10)]),i==10)' is false.
From what I can say with my puny test cases, you are 72% mainstream
open64 4.2.3@x86_64-suse-linux
We like to think that:
..05 int has the size of pointers
but 'sizeof(int)==sizeof(void*)' is false.
..08 overshifting is okay
but '(1<<bits_per_int)==0' is false.
..09a minus shifts backwards
but '(t=-1,(15<<t)==7)' is false.
..15 structs are packed
but 'sizeof(char_int)==(sizeof(char)+sizeof(int))' is false.
..17 size_t is unsigned int
but 'sizeof(size_t)==sizeof(unsigned int)' is false.
..21a Function Arguments are evaluated right to left
but '(gobble_args(0,ltr_fun(1),ltr_fun(2),ltr_fun(3),ltr_fun(4)),ltr_result==4321)' is false.
ltr_result is 1234 in this case
..25a pointer arithmetic works outside arrays
but '(diff=&p1-&p2, &p2+diff==&p1)' is false.
..26 sizeof() does not evaluate its arguments
but '(i=10,sizeof(char[((i=20),10)]),i==10)' is false.
From what I can say with my puny test cases, you are 75% mainstream
intel 11.1@x86_64-suse-linux
We like to think that:
..05 int has the size of pointers
but 'sizeof(int)==sizeof(void*)' is false.
..08 overshifting is okay
but '(1<<bits_per_int)==0' is false.
..09a minus shifts backwards
but '(t=-1,(15<<t)==7)' is false.
..14 i++ is strictly left to right
but '(i=0,a[i++]=i,a[0]==1)' is false.
..15 structs are packed
but 'sizeof(char_int)==(sizeof(char)+sizeof(int))' is false.
..17 size_t is unsigned int
but 'sizeof(size_t)==sizeof(unsigned int)' is false.
..21a Function Arguments are evaluated right to left
but '(gobble_args(0,ltr_fun(1),ltr_fun(2),ltr_fun(3),ltr_fun(4)),ltr_result==4321)' is false.
ltr_result is 1234 in this case
..26 sizeof() does not evaluate its arguments
but '(i=10,sizeof(char[((i=20),10)]),i==10)' is false.
From what I can say with my puny test cases, you are 75% mainstream
Turbo C++/DOS/Small Memory
We like to think that:
..09a minus shifts backwards
but '(t=-1,(15<<t)==7)' is false.
..16 malloc()=NULL means out of memory
but '(malloc(0)!=NULL)' is false.
..19-2 short<int
but 'sizeof(short)<sizeof(int)' is false.
..22 floating point is always IEEE
but 'STDC_IEC_559_is_defined' is false.
..25 pointer arithmetic works outside arrays
but '(diff=&var.int2-&var.int1, &var.int1+diff==&var.int2)' is false.
..25a pointer arithmetic works outside arrays
but '(diff=&p1-&p2, &p2+diff==&p1)' is false.
From what I can say with my puny test cases, you are 81% mainstream
Turbo C++/DOS/Medium Memory
We like to think that:
..09a minus shifts backwards
but '(t=-1,(15<<t)==7)' is false.
..10 void* can store function pointers
but 'sizeof(void*)>=sizeof(void(*)())' is false.
..16 malloc()=NULL means out of memory
but '(malloc(0)!=NULL)' is false.
..19-2 short<int
but 'sizeof(short)<sizeof(int)' is false.
..22 floating point is always IEEE
but 'STDC_IEC_559_is_defined' is false.
..25 pointer arithmetic works outside arrays
but '(diff=&var.int2-&var.int1, &var.int1+diff==&var.int2)' is false.
..25a pointer arithmetic works outside arrays
but '(diff=&p1-&p2, &p2+diff==&p1)' is false.
From what I can say with my puny test cases, you are 78% mainstream
Turbo C++/DOS/Compact Memory
We like to think that:
..05 int has the size of pointers
but 'sizeof(int)==sizeof(void*)' is false.
..09a minus shifts backwards
but '(t=-1,(15<<t)==7)' is false.
..16 malloc()=NULL means out of memory
but '(malloc(0)!=NULL)' is false.
..19-2 short<int
but 'sizeof(short)<sizeof(int)' is false.
..20 ptrdiff_t and size_t have the same size
but '(sizeof(ptrdiff_t)==sizeof(size_t))' is false.
..22 floating point is always IEEE
but 'STDC_IEC_559_is_defined' is false.
..25 pointer arithmetic works outside arrays
but '(diff=&var.int2-&var.int1, &var.int1+diff==&var.int2)' is false.
..25a pointer arithmetic works outside arrays
but '(diff=&p1-&p2, &p2+diff==&p1)' is false.
From what I can say with my puny test cases, you are 75% mainstream
cl65@Commodore PET (vice emulator)
I'll be updating these later:
Borland C++ Builder 6.0 on Windows XP
..04 a char is signed
but 'CHAR_MIN==SCHAR_MIN' is false.
..08 overshifting is okay
but '(1<<bits_per_int)==0' is false.
..09 overshifting is *always* okay
but '(1<<BITS_PER_INT)==0' is false.
..09a minus shifts backwards
but '(t=-1,(15<<t)==7)' is false.
..15 structs are packed
but 'sizeof(char_int)==(sizeof(char)+sizeof(int))' is false.
..16 malloc()=NULL means out of memory
but '(malloc(0)!=NULL)' is false.
..19-3 int<long
but 'sizeof(int)<sizeof(long)' is false.
..22 floating point is always IEEE
but 'STDC_IEC_559_is_defined' is false.
From what I can say with my puny test cases, you are 71% mainstream
Visual Studio Express 2010 C++ CLR, Windows 7 64bit
(must be compiled as C++ because the CLR compiler does not support pure C)
We like to think that:
..08 overshifting is okay
but '(1<<bits_per_int)==0' is false.
..09a minus shifts backwards
but '(t=-1,(15<<t)==7)' is false.
..14 i++ is structly left to right
but '(i=0,a[i++]=i,a[0]==1)' is false.
..15 structs are packed
but 'sizeof(char_int)==(sizeof(char)+sizeof(int))' is false.
..19-3 int<long
but 'sizeof(int)<sizeof(long)' is false.
..22 floating point is always IEEE
but 'STDC_IEC_559_is_defined' is false.
From what I can say with my puny test cases, you are 78% mainstream
MINGW64 (gcc-4.5.2 prerelase)
-- http://mingw-w64.sourceforge.net/
We like to think that:
..05 int has the size of pointers
but 'sizeof(int)==sizeof(void*)' is false.
..05a long has at least the size of pointers
but 'sizeof(long)>=sizeof(void*)' is false.
..08 overshifting is okay
but '(1<<bits_per_int)==0' is false.
..09a minus shifts backwards
but '(t=-1,(15<<t)==7)' is false.
..14 i++ is structly left to right
but '(i=0,a[i++]=i,a[0]==1)' is false.
..15 structs are packed
but 'sizeof(char_int)==(sizeof(char)+sizeof(int))' is false.
..17 size_t is unsigned int
but 'sizeof(size_t)==sizeof(unsigned int)' is false.
..19-3 int<long
but 'sizeof(int)<sizeof(long)' is false.
..22 floating point is always IEEE
but 'STDC_IEC_559_is_defined' is false.
From what I can say with my puny test cases, you are 67% mainstream
64 bit Windows uses the LLP64 model: Both int and long are defined as 32-bit, which means that neither is long enough for a pointer.
avr-gcc 4.3.2 / ATmega168 (Arduino Diecimila)
The failed assumptions are:
..14 i++ is structly left to right
..16 malloc()=NULL means out of memory
..19-2 short<int
..21 Evaluation is left to right
..22 floating point is always IEEE
The Atmega168 has a 16 bit PC, but code and data are in separate address spaces. Larger Atmegas have a 22 bit PC!.
gcc 4.2.1 on MacOSX 10.6, compiled with -arch ppc
We like to think that:
..09a minus shifts backwards
but '(t=-1,(15<<t)==7)' is false.
..13 The smallest bits come always first
but '(t=0x1234,0x34==*(char*)&t)' is false.
..14 i++ is structly left to right
but '(i=0,a[i++]=i,a[0]==1)' is false.
..15 structs are packed
but 'sizeof(char_int)==(sizeof(char)+sizeof(int))' is false.
..19-3 int<long
but 'sizeof(int)<sizeof(long)' is false.
..22 floating point is always IEEE
but 'STDC_IEC_559_is_defined' is false.
From what I can say with my puny test cases, you are 78% mainstream
A long time ago, I was teaching C from a textbook that had
printf("sizeof(int)=%d\n", sizeof(int));
as a sample question. It failed for a student, because sizeof yields values of type size_t, not int, int on this implementation was 16 bits and size_t was 32, and it was big-endian. (The platform was Lightspeed C on 680x0-based Macintoshes. I said it was a long time ago.)
You need to include the ++ and -- assumptions people make.
a[i++]= i;
For example, is syntactically legal, but produces varying results depending on too many things to reason out.
Any statement that has ++ (or --) and a variable which occurs more than once is a problem.
Very interesting!
Other things I can think of it might be useful to check for:
do function pointers and data pointers exist in the same address space? (Breaks in Harvard architecture machines like DOS small mode. Don't know how you'd test for it, though.)
if you take a NULL data pointer and cast it to the appropriate integer type, does it have the numeric value 0? (Breaks on some really ancient machines --- see http://c-faq.com/null/machexamp.html.) Ditto with function pointer. Also, they may be different values.
does incrementing a pointer past the end of its corresponding storage object, and then back again, cause sensible results? (I don't know of any machines this actually breaks on, but I believe the C spec does not allow you to even think about pointers that don't point to either (a) the contents of an array or (b) the element immediately after the array or (c) NULL. See http://c-faq.com/aryptr/non0based.html.)
does comparing two pointers to different storage objects with < and > produce consistent results? (I can imagine this breaking on exotic segment-based machines; the spec forbids such comparisons, so the compiler would be entitled to compare the offset part of the pointer only, and not the segment part.)
Hmm. I'll try and think of some more.
Edit: Added some clarifying links to the excellent C FAQ.
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