first app

#import <Foundation/Foundation.h>int main(int argc, const char * argv[])
{NSAutoreleasePool *pool = [NSAutoreleasePool new];NSLog(@"first start");[pool drain];return 0;
}

tech

1. 专注于概念，而不是迷失在语言技术细节中
2. 编程语言的目的是成为一个更好的程序员; 也就是说，在设计和实现新系统以及维护旧系统方面变得更加有效

the basic structure of objc program has

1. header preprocess
2. interface
3. implementation
4. method
5. variable
6. declare and expression
7. comment

use interface and implementation

#import <Foundation/Foundation.h>@interface SampleClass:NSObject
- (void)sampleMethod;
@end@implementation SampleClass
- (void)sampleMethod
{NSLog(@"hello from sample class");
}
@endint main()
{SampleClass *sampleClass = [[SampleClass alloc]init];[sampleClass sampleMethod];return 0;
}

type system

1. basic integer set and float set
2. enum type
3. void type
4. derive type include pointer, array, struct, union, function

// so far we still use Foundation
int main()
{NSLog(@"type int takes %d\n",sizeof(int));NSLog(@"Storage size for float : %d , maxval=%f \n", sizeof(float), FLT_MAX);int c_i = 1;NSInteger i = 1;NSLog(@"%d\n",i);
}

support c type variable and c type function

void test()
{printf("this is c type function\n");
}#define DEBUG YES
const int G_error_no = 1;// notice that upper case of const is a good style 
int main()
{  test();// cosume the c type functionNSLog(@"err no: %d\n",G_error_no);
}

基本运算符(算术，逻辑,位运算)的支持是和c保持一致，这里比较简单

1. https://www.yiibai.com/objective_c/objective_c_operators.html#article-start

method in objc

• (return_type) method_name:( argumentType1 )argumentName1
  joiningArgument2:( argumentType2 )argumentName2 …
  joiningArgumentn:( argumentTypen )argumentNamen {
  body of the function
  }

// skip the class declare and impl
// notice that java style is good style
// and joiningArgument just needed to take its place,but not a real name of argument
-(int)max:(int)num1 secondNumber:(int)num2{if (num1 > num2)return num1;else return num2;
}int main(){// call the method,for example using a classSampleClass *sampleClass = [[SampleClass alloc]init];int ret = [sampleClass max:1 secondNumber:2];printf("%d\n",ret);
}
// 函数参数按值传参和按引用/指针传参是支持的，有机会在深入一遍c语言

[deprecate] block is an instance (some error with enable blocks using -fblocks)[notfix]

仅表示单个任务或行为单元而不是方法集合是有意义的(using block),它允许创建不同的代码段，这些代码段可以传递给方法或函数，就像它们是值一样。 块是Objective-C对象，因此它们可以添加到NSArray或NSDictionary等集合中。 它们还能够从封闭范围中捕获值，使其类似于其他编程语言中的闭包或lambda

returntype (^blockName)(argumentType);

returntype (^blockName)(argumentType)= ^{
};

demo

#import <stdio.h>
#import <Foundation/Foundation.h>int main()
{NSAutoreleasePool *pool = [NSAutoreleasePool new];printf("yas\n");id undef = nil;if (undef == nil){printf("undef is nil\n");}float versionNumber = [NSString version]; printf("%f\n",versionNumber);NSString *w = @"Brainstorm";NSString * gprChannel = [NSString stringWithFormat:@"let me be %d",1];// use c style string char * c_str = "yes";NSString *str = [NSString stringWithCString:c_str];// convert c string to NSString classNSLog(@"%@",str);NSMutableString *s = AUTORELEASE ([NSMutableString new]);// Note. Static strings created with the @"..." construct are always immutable. [pool drain];return 0;
}

simple read file

#include <Foundation/Foundation.h>
#include <stdio.h>int
main (void)
{CREATE_AUTORELEASE_POOL(pool);NSString *string;NSString *filename = @"/home/etcix/hello-objc/test.txt";string = [NSString stringWithContentsOfFile: filename];if (string == nil){NSLog (@"Problem reading file %@", filename);/** <missing code: do something to manage the error...>* <exit perhaps ?>*/}else {printf("read file ok\n");}/** <missing code: do something with string...>*/RELEASE(pool);return 0;
}

examples

1. methods

#import <Foundation/Foundation.h>
#include <stdio.h>// interface
@interface SampleClass:NSObject
{//all variable in hereint age;
}@property(nonatomic) int age;//property可选聚合参数:readonly,assign,retain,atomic,readwrite(默认)
-(int)max:(int)lhs rhs:(int)rhs;//name of method is `max: rhs:`,usage:max: 1 rhs: 2 
@end// impl 
@implementation SampleClass@synthesize age;//动态生成get,set,注意要和属性名字一样，先property后synthesize-(int)max:(int)lhs rhs:(int)rhs
{return lhs>rhs ? lhs : rhs;
}
@endint main()
{SampleClass *sample = SampleClass.new;// 点语法调用，通常是在@property的属性上调用，其他方法一般不可用,而且区别于c++的是，sample是指针，但是访问属性却是点语法int a,b;printf("two integer value should input\n");scanf("%d %d",&a,&b);int ret = [sample max:a rhs: b];printf("the ret is %d\n",ret);sample.age = 1;//setprintf("%d\n",sample.age);//getreturn 0;
}

2. NSNumber

#import <Foundation/Foundation.h>
#import <stdio.h>@interface SampleClass:NSObject
-(NSNumber *)multiplyA:(NSNumber *)a withB:(NSNumber *)b; 
@end // impl
@implementation SampleClass
-(NSNumber *)multiplyA:(NSNumber *)a withB:(NSNumber *)b 
{float number1 = [a floatValue];float number2 = [b floatValue];float product = number1 * number2;NSNumber * result = [NSNumber numberWithFloat:product];return result;
}
@endint main()
{CREATE_AUTORELEASE_POOL(pool);SampleClass *sample = [[SampleClass alloc] init];NSNumber *a = [NSNumber numberWithFloat:5.6];NSNumber *b = [NSNumber numberWithFloat:1.6];NSNumber *res = [sample multiplyA:a withB:b];NSString *str = [res stringValue];NSLog(@"the res is %@",str);// 可见objc语法的冗长，但也证明了类型丰富RELEASE(pool);return 0;
}

3. array

#import <Foundation/Foundation.h>
#import <stdio.h>@interface SampleClass:NSObject
-(int *)getRandom;
@end // impl
@implementation SampleClass
-(int *)getRandom 
{static int arr[10];int i;srand((unsigned)time(NULL));for(i = 0; i< 10;++i){arr[i] = rand();NSLog(@"r[%d] = %d\n",i,arr[i]);}return arr;//return array
}
@endint main()
{CREATE_AUTORELEASE_POOL(pool);int *p;SampleClass *sample = [[SampleClass alloc] init];p = [sample getRandom];// cosume generated array// int i;for(int i = 0; i < 10; i++){NSLog(@"*(p+%d):%d\n",i,*(p + i));//use pointer of array}RELEASE(pool);return 0;
}

4. 指针

   int  var1;char var2[10];NSLog(@"Address of var1 variable: %x\n", &var1 );NSLog(@"Address of var2 variable: %x\n", &var2 );int  var = 20;    /* 变量定义 */int  *ip;         /* 指针变量声明 */  ip = &var;       /* 在指针变量中存储 var 的地址*/NSLog(@"Address of var variable: %x\n", &var  );/* 存储在指针变量中的地址 */NSLog(@"Address stored in ip variable: %x\n", ip );/* 使用指针访问该值 */NSLog(@"Value of *ip variable: %d\n", *ip );

5. 字符串

NSString *str1 = @"hello";NSString *str2 = @"world";NSString *str3;int len;str3 = [str2 uppercaseString];NSLog(@"str3: %@",str3);str3 = [str1 stringByAppendingFormat:@" append to str1"];NSLog(@"str3: %@",str3);len = [str3 length];NSLog(@"str3: %@,len: %d",str3,len);

6. 有机会完善对Foundation的使用吧，记住上面的链接足够入门了
7. 感兴趣的方向可能是拿它做server side吧

[important] my code style using application.make

1. GNUmakefile

# !!!NOTE: this is application makefile for simple project, read it and just modify a little
GNUSTEP_MAKEFILES = /usr/share/GNUstep/MakefilesSRC_DIR = . # this folder is source code directory, CAN MODIFY 
include ${GNUSTEP_MAKEFILES}/common.make
APP_NAME = main # name of application，CAN MODIFY
${APP_NAME}_HEADER_FILES = 
${APP_NAME}_OBJC_FILES = $(SRC_DIR)/*.m #every .m file will be matched, CAN MODIFY
${APP_NAME}_RESOURCE_FILES =
include ${GNUSTEP_MAKEFILES}/application.make

2. r.sh for simple run script or r.bat on windows

#r.sh
# I am not going to provide r.bat
make
openapp ./main.app #this name refer to GNUmakefile APP_NAME

3. simple project文件结构

.
├── GNUmakefile
├── main.m
├── Person.m
├── readme.md
└── r.sh
# 如果复杂可以添加文件夹
# 对于每一个.h .m的配对，我认为如果是简单的类的话，直接写成.m就可以了，不要写头文件了
# .m文件都应该是import,少用include

4. 其他非application项目，如tool(command line tool)项目，我也提供一个参考的GNUmakefile吧

#GNUmakefile for toolGNUSTEP_MAKEFILES=/usr/share/GNUstep/Makefiles #on linux mintinclude  ${GNUSTEP_MAKEFILES}/common.make
TOOL_NAME = client # MODIFY
${TOOL_NAME}_HEADER_FILES = # ADD 
${TOOL_NAME}_OBJC_FILES = client.m # MODIFY
include ${GNUSTEP_MAKEFILES}/tool.make
# still run for example
# make && ./obj/client

对GNUstep和objc的其他说明

1. 在c上添加的东西:类，协议，id和nil，OO里的他基本也有，消息传送到对象的机制
2. 他留存的生命力: Foundation + 完全兼容c语言 + 一些小小组件，但是可能增加复杂度，比如makefile的编写
3. NSObject更像一个java接口，c++抽象类，就是他的很多方法可以被重写，也可以被继承者直接使用

code reference

• the above link