char数组初始化第一个元素，那么剩下的就是0；否则就是乱码。为什么?

kgisme170

#include<stdio.h>
int main(void){
  char buf[128];//这里没有初始化
  for(int i=0;i<128;++i){
   printf("%c",buf[i]);
  }
  return 0;
}
打印出一堆乱码

但是如果我把第2行改成char buf[128]={'0'};
那么就打印出一个0。似乎这种情况下buf剩下的元素会被初始化为0(也就是字符串结束符)。为什么最原始的代码，buf的内容没有被初始化呢?

我在Sun的CC和Visual C++ 2008都尝试过了，都是一样的结果。
这个是C/C++标准规定的吗，数组什么时候初始化什么时候不初始化?

谢谢！！！！！

caboy_cu

栈上的数组永远不会初始化

alleva

栈上的数组永远不会初始化
caboy_cu 发表于 2010-08-31 18:03

   

char c = 'a';不是初始化吗?不初始化怎么计算?

caboy_cu

char c = 'a';不是初始化吗?不初始化怎么计算?
alleva 发表于 2010-08-31 18:13

不好意思，少了2字，永远不会自动初始化

tempname2

在Java里这样编译就不能通过了。。。。。。。

hellioncu

char buf[128]={'0'};这样是全部初始化为0

幻の上帝

对于char之类的scalar type为元素类型的数组初始化时，没显式在初始化列表中出现的元素会默认置0。

C++03：

8.5.1
1 An aggregate is an array or a class (clause 9) with no user-declared constructors (12.1), no private or protected
non-static data members (clause 11), no base classes (clause 10), and no virtual functions (10.3).
2 When an aggregate is initialized the initializer can contain an initializer-clause consisting of a braceenclosed,
comma-separated list of initializer-clauses for the members of the aggregate, written in increasing
subscript or member order. If the aggregate contains subaggregates, this rule applies recursively to the members of the subaggregate.
7 If there are fewer initializers in the list than there are members in the aggregate, then each member not
explicitly initialized shall be value-initialized (8.5).

8.5
5 To zero-initialize an object of type T means:
— if T is a scalar type (3.9), the object is set to the value of 0 (zero) converted to T;
— if T is a non-union class type, each nonstatic data member and each base-class subobject is zeroinitialized;
— if T is a union type, the object’s first named data member89) is zero-initialized;
— if T is an array type, each element is zero-initialized;
— if T is a reference type, no initialization is performed.
To default-initialize an object of type T means:
— if T is a non-POD class type (clause 9), the default constructor for T is called (and the initialization is
ill-formed if T has no accessible default constructor);
— if T is an array type, each element is default-initialized;
— otherwise, the object is zero-initialized.
To value-initialize an object of type T means:
— if T is a class type (clause 9) with a user-declared constructor (12.1), then the default constructor for T is
called (and the initialization is ill-formed if T has no accessible default constructor);
— if T is a non-union class type without a user-declared constructor, then every non-static data member
and base-class component of T is value-initialized;
__________________
89) This member must not be static, by virtue of the requirements in 9.5.
145

— if T is an array type, then each element is value-initialized;
— otherwise, the object is zero-initialized
A program that calls for default-initialization or value-initialization of an entity of reference type is illformed.
If T is a cv-qualified type, the cv-unqualified version of T is used for these definitions of zeroinitialization,
default-initialization, and value-initialization.

C99：
6.7.8
10 If an object that has automatic storage duration is not initialized explicitly, its value is
indeterminate. If an object that has static storage duration is not initialized explicitly,
then:
— if it has pointer type, it is initialized to a null pointer;
— if it has arithmetic type, it is initialized to (positive or unsigned) zero;
— if it is an aggregate, every member is initialized (recursively) according to these rules;
— if it is a union, the first named member is initialized (recursively) according to these
rules.

efolzl

龟腚~

liwangli1983

即使你写成char buf[128]={'1'}; 其它的仍然被初始化为0