iphone - 字符串分配和初始化

Question

可能重复：
iPhone Dev - NSString Creation

我在用

 NSString   *str_Message; 
if ([txt_NoOfPersons.text length] == 0){
    bln_Validate  = FALSE;
    str_Message  = [[NSString alloc]initWithString:@"Number of Persons field is required."];
}
else if ([txt_NoOfPersons.text intValue] == 0)
{
    bln_Validate  = FALSE;
    str_Message  = [[NSString alloc]initWithString:@"Please enter your guest count."];}
}
if ([txt_DateAndTime.text length] == 0)
{
    bln_Validate  = FALSE;
    str_Message  = [[NSStrin@"Date and Time field is required."];

}    

如果我使用Nsstring *str_Message=nil; '

if ([txt_NoOfPersons.text length] == 0)
{
    bln_Validate  = FALSE;
    str_Message  = @"Number of Persons field is required.";
}
else if ([txt_NoOfPersons.text intValue] == 0)
{
    bln_Validate  = FALSE;
    str_Message  = @"Please enter your guest count.";

}

那么Nsstring *str;之间的效果和区别是什么？字符串 *str=nil

Answer 1

NSString *str;使用 ARC 时，和之间没有区别NSString *str = nil;，所有指针在初始化时都保证为 nil。

当您不使用 ARC 时，指针可能指向垃圾值。