未初始化的变量常常会导致一些奇怪的bug，有时还真不好调式。养成在初始化变量的习惯有利于减少编程错误，提高程序质量。
C++提供了构造和析构函数，其中构造函数就是为初始化而设计的；对于内置变量（char,int,long等）的初始化C++无能为力，其默认行为是未初始化，故其值依赖于变量类型（是否为static）和编译器。
本文中将讨论两类基本变量：标量和数组，标量指单一变量，数组本质上就是一整块内存空间(别忘了memset)。其他数据结构均基于这两类基本变量，一般由库提供，比如著名的C++ STL容器。
声明时初始化的格式直接参见代码中的注释。
1
#include
<
errno.h
>
2 #include < math.h >
3 #include < stdio.h >
4 #include < stdlib.h >
5 #include < string .h >
6
7 void Print( int * buf, int len)
8 {
9 printf( " Value(int)= " );
10 for ( int i = 0 ; i < len; ++ i)
11 {
12 printf( " %d " , buf[i]);
13 }
14 printf( " \n " );
15 }
16
17 void Print( char * buf, int len)
18 {
19 printf( " Value(char)= " );
20 for ( int i = 0 ; i < len; ++ i)
21 {
22 printf( " %c " , buf[i]);
23 }
24 printf( " \n " );
25 }
26
27 int main( int argc, char ** argv)
28 {
29 printf( " scale variable:\n " );
30 // 1. scale variable
31 char v1; // not initialization. Value depends on compiler
32 Print( & v1, 1 );
33
34 char v2 = ' 1 ' ; // user initialization
35 Print( & v2, 1 );
36
37 char * v3 = new char ; // not initialization. Value depends on compiler
38 Print(v3, 1 );
39
40 char * v4 = new char (); // zeroing initialization. value is 0;
41 Print(v4, 1 );
42
43 char * v5 = new char ( ' A ' ); // user initialization
44 Print(v5, 1 );
45
46 int * i5 = new int ( 1243214 ); // user initialization
47 Print(i5, 1 );
48
49
50 printf( " array variable:\n " );
51 // 2. array
52 char a[ 10 ]; // not initialization. Value depends on compiler
53 Print(a, 10 );
54
55 char b[ 10 ] = {}; // same as {0}; zeroing initialization.
56 Print(b, 10 );
57
58 char b1[ 10 ] = { ' a ' }; // b[0]='a', other is 0!
59 Print(b1, 10 );
60
61 char * c = new char [ 10 ]; // not initialization. Value depends on compiler
62 Print(c, 10 );
63
64 char * d = new char [ 10 ](); // zeroing initialization. 经 追海逐风 证实，g++无此功能
65 Print(d, 10 );
66
67 // char* e = new char[10]('a'); // Error: ISO C++ forbids initialization in array new
68 // Print(e, 10);
69
70 return 0 ;
71 }
72
2 #include < math.h >
3 #include < stdio.h >
4 #include < stdlib.h >
5 #include < string .h >
6
7 void Print( int * buf, int len)
8 {
9 printf( " Value(int)= " );
10 for ( int i = 0 ; i < len; ++ i)
11 {
12 printf( " %d " , buf[i]);
13 }
14 printf( " \n " );
15 }
16
17 void Print( char * buf, int len)
18 {
19 printf( " Value(char)= " );
20 for ( int i = 0 ; i < len; ++ i)
21 {
22 printf( " %c " , buf[i]);
23 }
24 printf( " \n " );
25 }
26
27 int main( int argc, char ** argv)
28 {
29 printf( " scale variable:\n " );
30 // 1. scale variable
31 char v1; // not initialization. Value depends on compiler
32 Print( & v1, 1 );
33
34 char v2 = ' 1 ' ; // user initialization
35 Print( & v2, 1 );
36
37 char * v3 = new char ; // not initialization. Value depends on compiler
38 Print(v3, 1 );
39
40 char * v4 = new char (); // zeroing initialization. value is 0;
41 Print(v4, 1 );
42
43 char * v5 = new char ( ' A ' ); // user initialization
44 Print(v5, 1 );
45
46 int * i5 = new int ( 1243214 ); // user initialization
47 Print(i5, 1 );
48
49
50 printf( " array variable:\n " );
51 // 2. array
52 char a[ 10 ]; // not initialization. Value depends on compiler
53 Print(a, 10 );
54
55 char b[ 10 ] = {}; // same as {0}; zeroing initialization.
56 Print(b, 10 );
57
58 char b1[ 10 ] = { ' a ' }; // b[0]='a', other is 0!
59 Print(b1, 10 );
60
61 char * c = new char [ 10 ]; // not initialization. Value depends on compiler
62 Print(c, 10 );
63
64 char * d = new char [ 10 ](); // zeroing initialization. 经 追海逐风 证实，g++无此功能
65 Print(d, 10 );
66
67 // char* e = new char[10]('a'); // Error: ISO C++ forbids initialization in array new
68 // Print(e, 10);
69
70 return 0 ;
71 }
72
