字符串分配和初始化

Question

可能重复：
iPhone Dev - NSString Creation

我使用

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."]; 

}  

insted的的，如果我使用的NSString * str_Message =零;'

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."; 

} 

那么会是怎样的效果是什么的NSString *海峡之间的差异; Nsstring * str = nil

Answer 1

当使用ARC时，NSString *str;和NSString *str = nil;之间没有区别，所有指针在初始化时保证为零。

当您不使用ARC时，指针可能指向垃圾值。