Is this defined?

rosynirvana

例子来自
http://coolshell.cn/articles/5761.html
的最后一段代码

1. #include <stdio.h>
   
2. int main(void)
   
3. {
   
4.     int a[5];
   
5.     printf("%x\n", &a+1);
   
6. }

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C99 6.5.6.8

When an expression that has integer type is added to or subtracted from a pointer, the
result has the type of the pointer operand. If the pointer operand points to an element of
an array object, and the array is large enough, the result points to an element offset from
the original element such that the difference of the subscripts of the resulting and original
array elements equals the integer expression.  ... otherwise, the
behavior is undefined.

6.5.6.10还有一个例子

1. {
   
2. int n = 4, m = 3;
   
3. int a[n][m];
   
4. int (*p)[m] = a; // p == &a[0]
   
5. p += 1; // p == &a[1]
   
6. (*p)[2] = 99; // a[1][2] == 99
   
7. n=p-a; //n==1
   
8. }

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于是，如果a是二维数组，a+1明显是有定义的；但是原例子中的a是一维数组，那么&a+1是否是有定义的行为呢

hbmhalley

回复 1# rosynirvana


   

于是，如果a是二维数组，&a+1明显是有定义的；

    啥逻辑?
    a+1 是有定义的
    &a+1 是毛

rosynirvana

回复 2# hbmhalley
my bad
笔误

   

hbmhalley

回复 3# rosynirvana


    帮你问了问

    c99 6.5.6-7

For the purposes of these operators, a pointer to an object that is not an element of an array behaves the same as a pointer to the first element of an array of length one with the type of the object as its element type.

rosynirvana

回复 4# hbmhalley


    谢谢，明白了

captivated

回复 2# hbmhalley


    int a[5];

a 的类型是数组类型, 在作为函数参数时退化为int *类型.
&a 的类型是 int (*)[5].

&&a不合法.

===================

1. 
   
2. #include <stdio.h>
   
3. 
   
4. void foo(int *p, int len)
   
5. {
   
6. 
   
7. }
   
8. 
   
9. int main(void)
   
10. {
    
11.     int a[5];
    
12.     foo(&a, 5);
    
13. 
    
14.     return 0;
    
15. }

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===================

gcc的warning:

type.c: In function ‘main’:
type.c:12: warning: passing argument 1 of ‘foo’ from incompatible pointer type
type.c:3: note: expected ‘int *’ but argument is of type ‘int (*)[5]’

===================

gcc的版本:

root@captivated:/home/tmp# gcc -v
Using built-in specs.
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu 4.4.3-4ubuntu5.1' --with-bugurl=file:///usr/share/doc/gcc-4.4/README.Bugs --enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr --enable-shared --enable-multiarch --enable-linker-build-id --with-system-zlib --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.4 --program-suffix=-4.4 --enable-nls --enable-clocale=gnu --enable-libstdcxx-debug --enable-plugin --enable-objc-gc --disable-werror --with-arch-32=i486 --with-tune=generic --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 4.4.3 (Ubuntu 4.4.3-4ubuntu5.1)