Question

我在objective-c中有以下代码，并带有警告。我审查的帖子似乎暗示这不是一个大问题;它是一种自动创建的方法。在我的情况下，如果应该不给出结果。我不确定我做错了什么。鉴于这是我正在做的Objective-C中的前几个程序之一，我想验证它，以便我熟悉正确的语法。这是代码：

#import <stdio.h>
#import <objc/Object.h>
//---------------interface section-------------

@interface Fraction: Object
{
  int numerator;
  int denominator;
}
-(void) setNumerator: (int) n;
-(void) setDenominator: (int) d;
-(void) print;
@end
//-----------------implementation section-------
@implementation Fraction;
//getters
-(int) numerator
{
  return numerator;
}
-(int) denominator
{
  return denominator;
}
//setters
-(void) setNumerator: (int) num
{
  numerator = num;
}
-(void) setDenominator: (int) denom
{
  denominator = denom;
}
-(void) print
{
  printf("The value of the fraction is %i/%i\n", numerator, denominator);
}
@end
//-----------------program section-------------------------
int main (void)
{
  Fraction *myFract;
  myFract = [Fraction new];
  [myFract setNumerator: 1];
  [myFract setDenominator: 3];

  printf ("The numerator is %i, and the denominator is %i\n", [myFract numerator], [myFract denominator]);
  [myFract print];
  [myFract free];
  return 0;
}

以下是警告信息：

$ gcc -o fraction fraction.m -I /GNUstep/System/Library/Headers -L /GNUstep/System/Library/Libraries -lobjc -lgnustep-b
ase -fconstant-string-class=NSConstantString
fraction.m: In function 'main':
fraction.m:43:3: warning: 'Fraction' may not respond to '+new' [enabled by default]
fraction.m:43:3: warning: (Messages without a matching method signature [enabled by default]
fraction.m:43:3: warning: will be assumed to return 'id' and accept [enabled by default]
fraction.m:43:3: warning: '...' as arguments.) [enabled by default]
fraction.m:49:3: warning: 'Fraction' may not respond to '-free' [enabled by default]

这是输出：

$ ./fraction.exe
The numerator is 0, and the denominator is 0

不确定它是否相关，但我使用GNUstep进行编译。我不知道如何在其上运行调试。我尝试了GDB，但它没有用。顺便说一下，如果我想充分利用这种语言的好处，我是否需要Mac环境？这种语言是否有非Mac / Apple应用程序？

Answer 1

Object是一个已弃用的根类。请改用NSObject。不要致电free。如果您使用的是手动内存管理，请使用release。如果您使用的是ARC，请不要拨打任何电话。

new不必支持

GNUstep，因此您应使用课程alloc和init模式。

@interface Fraction: NSObject
{
    int numerator;
    int denominator;
}
-(void) setNumerator: (int) n;
-(void) setDenominator: (int) d;
-(void) print;
@end
//-----------------implementation section-------
@implementation Fraction;
//getters
-(int) numerator
{
    return numerator;
}
-(int) denominator
{
    return denominator;
}
//setters
-(void) setNumerator: (int) num
{
    numerator = num;
}
-(void) setDenominator: (int) denom
{
    denominator = denom;
}
-(void) print
{
    printf("The value of the fraction is %i/%i\n", numerator, denominator);
}
@end
//-----------------program section-------------------------
int main (void)
{
    Fraction *myFract = [[Fraction alloc] init];
    [myFract setNumerator: 1];
    [myFract setDenominator: 3];

    printf ("The numerator is %i, and the denominator is %i\n", [myFract numerator], [myFract denominator]);
    [myFract print];
    [myFract release];
    return 0;
}

您还可以使用属性进行简化，以下是带有自动引用计数的Obj-C 2.0语法。

@interface Fraction: NSObject

@property (nonatomic, assign) int numerator;
@property (nonatomic, assign) int denominator;

- (void)print;

@end

@implementation Fraction
- (void)print {
   printf("The value of the fraction is %i/%i\n", self.numerator, self.denominator);
}
@end

int main (void)
{
    Fraction *myFract = [[Fraction alloc] init];
    myFract.numerator = 1;
    myFract.denominator = 3;

    printf ("The numerator is %i, and the denominator is %i\n", [myFract numerator], [myFract denominator]);
    [myFract print];
    return 0;
}

即使使用GNUstep，您也应该使用Clang进行编译。 GCC不会再做了。

目标C未定义的新方法可能是问题

1 个答案: