c++中初始化和赋值操作差别是很大的。
对于基本数据类型差别不大：
比如：
int a = 12; // initialization, copy 0X000C to a
a = 12; // assignment, copy 0X000C to a
但是对用户自定义的数据类型比如String 初始化和赋值就差别很大：
class String {
public:
String( const char *init ); // intentionally not explicit!
~String();
String( const String &that );
String &operator =( const String &that );
String &operator =( const char *str );
void swap( String &that );
friend const String // concatenate
operator +( const String &, const String & );
friend bool operator <( const String &, const String & );
//...
private:
String( const char *, const char * ); // computational
char *s_;
};
初始化的构造过程比较简单：先分配一个足够大的空间然后填充上数据：
String::String( const char *init ) {
if( !init ) init = "";
s_ = new char[ strlen(init)+1 ];
strcpy( s_, init );
}
析构过程更简单：
String::~String() { delete [] s_; }
但是如果赋值操作就复杂多了：
String &String::operator =( const char *str ) {
if( !str ) str = "";
char *tmp = strcpy( new char[ strlen(str)+1 ], str );
delete [] s_;
s_ = tmp;
return *this;
}
看来在条件允许的情况下最好在初始化的时候就赋值，而尽量避免用=号赋值了。
相关链接：C++ Common Knowledge: Assignment and Initialization Are Different
