「程序9.1」中由Kochan編寫的「objective-c中的程序」的複製粘貼代碼。但它不編譯。錯誤:從不兼容類型分配void
有兩個類:Fraction和Complex。 Complex的對象似乎工作正常,但「main.m」中的Fraction的對象「fracResult」給出了一個錯誤:「從不兼容的類型'void'分配給」Fraction *「。
這裏是Fraction.h:
#import <Foundation/Foundation.h>
// Define the Fraction class
@interface Fraction : NSObject
{
int numerator;
int denominator;
}
@property int numerator, denominator;
-(void) print;
-(void) setTo: (int) n over: (int) d;
-(double) convertToNum;
-(void) add: (Fraction *) f;
-(void) reduce;
@end
Fraction.m文件:
#import "Fraction.h"
@implementation Fraction
@synthesize numerator, denominator;
-(void) print
{
NSLog (@"%i/%i", numerator, denominator);
}
-(double) convertToNum
{
if (denominator != 0)
return (double) numerator/denominator;
else
return NAN;
}
-(void) setTo: (int) n over: (int) d
{
numerator = n;
denominator = d;
}
// add a Fraction to the receiver
-(void) add: (Fraction *) f
{
// To add two fractions:
// a/b + c/d = ((a*d) + (b*c))/(b * d)
numerator = numerator * f.denominator + denominator * f.numerator;
denominator = denominator * f.denominator;
}
-(void) reduce
{
int u = numerator;
int v = denominator;
int temp;
while (v != 0) {
temp = u % v;
u = v;
v = temp;
}
numerator /= u;
denominator /= u;
}
@end
main.m文件:
#import "Fraction.h"
#import "Complex.h"
int main (int argc, char *argv[])
{
NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
Fraction *f1 = [[Fraction alloc] init];
Fraction *f2 = [[Fraction alloc] init];
Fraction *fracResult;
Complex *c1 = [[Complex alloc] init];
Complex *c2 = [[Complex alloc] init];
Complex *compResult;
[f1 setTo: 1 over: 10];
[f2 setTo: 2 over: 15];
[c1 setReal: 18.0 andImaginary: 2.5];
[c2 setReal: -5.0 andImaginary: 3.2];
// add and print 2 complex numbers
[c1 print]; NSLog (@" +"); [c2 print];
NSLog (@"---------");
compResult = [c1 add: c2];
[compResult print];
NSLog (@"\n");
[c1 release];
[c2 release];
[compResult release];
// add and print 2 fractions
[f1 print]; NSLog (@" +"); [f2 print];
NSLog (@"----");
fracResult= [f1 add: f2]; //this line gives an error
[fracResult print];
[f1 release];
[f2 release];
[fracResult release];
[pool drain];
return 0;
}
就此專題研究,我發現了通常,這種錯誤使用指針引起的錯誤類型。有人建議,簡單地從方法「add:」的聲明和實施中刪除星號。但是,這導致了更多的「語義問題」
此外,由於本書中使用的字符和xcode使用的字符不同,有時書中的代碼無法編譯。通常,短劃線是不同的。但是這也沒有解決「不兼容型」的問題。
歡迎任何建議或建議。
更正了它。謝謝。 –