From 3a495d7fa241391e8bf04f35d675f446f039a024 Mon Sep 17 00:00:00 2001
From: light-city <455954986@qq.com>
Date: Sun, 11 Aug 2019 13:24:05 +0800
Subject: [PATCH] update dir

---
 README.md           |   1 +
 macro/README.md     | 232 ++++++++++++++++++++++++++++++++++++++++++++
 macro/do_while      | Bin 0 -> 9464 bytes
 macro/do_while.cpp  |  76 +++++++++++++++
 macro/sig_examp     | Bin 0 -> 14360 bytes
 macro/sig_examp.cpp |  86 ++++++++++++++++
 6 files changed, 395 insertions(+)
 create mode 100644 macro/README.md
 create mode 100755 macro/do_while
 create mode 100644 macro/do_while.cpp
 create mode 100755 macro/sig_examp
 create mode 100644 macro/sig_examp.cpp

diff --git a/README.md b/README.md
index 2e99f93..516666b 100644
--- a/README.md
+++ b/README.md
@@ -29,6 +29,7 @@
 - [x] [enum那些事](./enum)
 - [x] [decltype那些事](./decltype)
 - [x] [引用与指针那些事](./pointer_refer)
+- [x] [宏那些事](./macro)
 
 代码运行：
  全部在linux下用vim编写，使用gcc/g++调试！全部可正常运行！
diff --git a/macro/README.md b/macro/README.md
new file mode 100644
index 0000000..d20b612
--- /dev/null
+++ b/macro/README.md
@@ -0,0 +1,232 @@
+# 宏那些事
+
+## 关于作者：
+
+个人公众号：
+
+![](../img/wechat.jpg)
+
+## 1.宏中包含特殊符号
+
+分为几种：`#`，`##`，`\`
+
+### 1.1 字符串化操作符（#）
+
+**在一个宏中的参数前面使用一个#,预处理器会把这个参数转换为一个字符数组**，换言之就是：**#是“字符串化”的意思，出现在宏定义中的#是把跟在后面的参数转换成一个字符串**。
+
+**注意：其只能用于有传入参数的宏定义中，且必须置于宏定义体中的参数名前。**
+
+例如：
+
+```c++
+#define exp(s) printf("test s is:%s\n",s)
+#define exp1(s) printf("test s is:%s\n",#s)
+#define exp2(s) #s 
+int main() {
+    exp("hello");
+    exp1(hello);
+
+    string str = exp2(   bac );
+    cout<<str<<" "<<str.size()<<endl;
+    /**
+     * 忽略传入参数名前面和后面的空格。
+     */
+    string str1 = exp2( asda  bac );
+    /**
+     * 当传入参数名间存在空格时，编译器将会自动连接各个子字符串，
+     * 用每个子字符串之间以一个空格连接，忽略剩余空格。
+     */
+    cout<<str1<<" "<<str1.size()<<endl;
+    return 0;
+}
+```
+
+上述代码给出了基本的使用与空格处理规则，空格处理规则如下：
+
+- 忽略传入参数名前面和后面的空格。
+
+```c++
+string str = exp2(   bac );
+cout<<str<<" "<<str.size()<<endl;
+```
+
+输出：
+
+```
+bac 3
+```
+
+- 当传入参数名间存在空格时，编译器将会自动连接各个子字符串，用每个子字符串之间以一个空格连接，忽略剩余空格。
+
+```c++
+string str1 = exp2( asda  bac );
+cout<<str1<<" "<<str1.size()<<endl;
+```
+
+输出：
+
+```
+asda bac 8
+```
+
+### 1.2 符号连接操作符（##）
+
+**“##”是一种分隔连接方式，它的作用是先分隔，然后进行强制连接。将宏定义的多个形参转换成一个实际参数名。**
+
+注意事项：
+
+**（1）当用##连接形参时，##前后的空格可有可无。**
+
+**（2）连接后的实际参数名，必须为实际存在的参数名或是编译器已知的宏定义。**
+
+**（3）如果##后的参数本身也是一个宏的话，##会阻止这个宏的展开。**
+
+示例：
+
+```c++
+
+#define expA(s) printf("前缀加上后的字符串为:%s\n",gc_##s)  //gc_s必须存在
+// 注意事项2
+#define expB(s) printf("前缀加上后的字符串为:%s\n",gc_  ##  s)  //gc_s必须存在
+// 注意事项1
+#define gc_hello1 "I am gc_hello1"
+int main() {
+    // 注意事项1
+    const char * gc_hello = "I am gc_hello";
+    expA(hello);
+    expB(hello1);
+}
+```
+
+### 1.3 续行操作符（\） 
+
+**当定义的宏不能用一行表达完整时，可以用”\”表示下一行继续此宏的定义。**
+
+**注意 \ 前留空格。**
+
+```c++
+#define MAX(a,b) ((a)>(b) ? (a) \
+   :(b))  
+int main() {
+    int max_val = MAX(3,6);
+    cout<<max_val<<endl;
+}
+```
+
+上述代码见：[sig_examp.cpp](sig_examp.cpp)
+
+## 2.do{...}while(0)的使用
+
+### 2.1 避免语义曲解
+
+例如：
+
+```
+#define fun() f1();f2();
+if(a>0)
+	fun()
+```
+
+这个宏被展开后就是：
+
+```
+if(a>0)
+	f1();
+	f2();
+```
+
+本意是a>0执行f1 f2，而实际是f2每次都会执行，所以就错误了。
+
+为了解决这种问题，在写代码的时候，通常可以采用`{}`块。
+
+如：
+
+```c++
+#define fun() {f1();f2();}
+if(a>0)
+	fun();
+// 宏展开
+if(a>0)
+{
+    f1();
+    f2();
+};
+```
+
+但是会发现上述宏展开后多了一个分号，实际语法不太对。(虽然编译运行没问题，正常没分号)。
+
+### 2.2避免使用goto控制流
+
+在一些函数中，我们可能需要在return语句之前做一些清理工作，比如释放在函数开始处由malloc申请的内存空间，使用goto总是一种简单的方法：
+
+```c++
+int f() {
+    int *p = (int *)malloc(sizeof(int));
+    *p = 10; 
+    cout<<*p<<endl;
+#ifndef DEBUG
+    int error=1;
+#endif
+    if(error)
+        goto END;
+    // dosomething
+END:
+    cout<<"free"<<endl;
+    free(p);
+    return 0;
+}
+```
+
+但由于goto不符合软件工程的结构化，而且有可能使得代码难懂，所以很多人都不倡导使用，这个时候我们可以使用do{...}while(0)来做同样的事情：
+
+```c++
+int ff() {
+    int *p = (int *)malloc(sizeof(int));
+    *p = 10; 
+    cout<<*p<<endl;
+    do{ 
+#ifndef DEBUG
+        int error=1;
+#endif
+        if(error)
+            break;
+        //dosomething
+    }while(0);
+    cout<<"free"<<endl;
+    free(p);
+    return 0;
+}
+```
+
+这里将函数主体部分使用do{...}while(0)包含起来，使用break来代替goto，后续的清理工作在while之后，现在既能达到同样的效果，而且代码的可读性、可维护性都要比上面的goto代码好的多了。
+
+### 2.3 避免由宏引起的警告
+
+内核中由于不同架构的限制，很多时候会用到空宏，。在编译的时候，这些空宏会给出warning，为了避免这样的warning，我们可以使用do{...}while(0)来定义空宏：
+
+```
+#define EMPTYMICRO do{}while(0)
+```
+
+### 2.4 **定义单一的函数块来完成复杂的操作**
+
+如果你有一个复杂的函数，变量很多，而且你不想要增加新的函数，可以使用do{...}while(0)，将你的代码写在里面，里面可以定义变量而不用考虑变量名会同函数之前或者之后的重复。
+这种情况应该是指一个变量多处使用（但每处的意义还不同），我们可以在每个do-while中缩小作用域，比如：
+
+```c++
+int fc()
+{
+    int k1 = 10;
+    cout<<k1<<endl;
+    do{
+        int k1 = 100;
+        cout<<k1<<endl;
+    }while(0);
+    cout<<k1<<endl;
+}
+```
+
+上述代码见：[do_while.cpp](do_while.cpp)
+
+学习文章：<https://www.cnblogs.com/lizhenghn/p/3674430.html>
+
diff --git a/macro/do_while b/macro/do_while
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diff --git a/macro/do_while.cpp b/macro/do_while.cpp
new file mode 100644
index 0000000..68af132
--- /dev/null
+++ b/macro/do_while.cpp
@@ -0,0 +1,76 @@
+#include <iostream>
+#include <malloc.h>
+
+using namespace std;
+#define f1() cout<<"f1()"<<endl;
+#define f2() cout<<"f2()"<<endl;
+
+#define fun() {f1();f2();}
+#define fun1() \
+    do{ \
+        f1();\
+        f2();\
+    }while(0)
+
+int f() {
+    int *p = (int *)malloc(sizeof(int));
+    *p = 10;
+    cout<<*p<<endl;
+#ifndef DEBUG
+    int error=1;
+#endif
+    if(error)
+        goto END;
+
+    // dosomething
+END:
+    cout<<"free"<<endl;
+    free(p);
+    return 0;
+}
+
+int ff() {
+
+    int *p = (int *)malloc(sizeof(int));
+    *p = 10;
+    cout<<*p<<endl;
+
+    do{
+#ifndef DEBUG
+        int error=1;
+#endif
+        if(error)
+            break;
+        //dosomething
+    }while(0);
+
+    cout<<"free"<<endl;
+    free(p);
+    return 0;
+}
+
+
+int fc()
+{
+    int k1 = 10;
+    cout<<k1<<endl;
+    do{
+        int k1 = 100;
+        cout<<k1<<endl;
+    }while(0);    
+    cout<<k1<<endl;
+}
+
+int main() {
+
+    if(1>0)
+        fun();
+
+    if(2>0)
+        fun1();
+
+    f();
+    ff();
+    fc();
+    return 0;
+}
diff --git a/macro/sig_examp b/macro/sig_examp
new file mode 100755
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diff --git a/macro/sig_examp.cpp b/macro/sig_examp.cpp
new file mode 100644
index 0000000..85290a7
--- /dev/null
+++ b/macro/sig_examp.cpp
@@ -0,0 +1,86 @@
+#include <iostream>
+#include <string>
+#include <cstring>
+#include <stdio.h>
+
+using namespace std;
+
+///===========================================
+/**
+ * (#)字符串操作符
+ */
+///===========================================
+#define exp(s) printf("test s is:%s\n",s)
+#define exp1(s) printf("test s is:%s\n",#s)
+
+#define exp2(s) #s 
+
+
+///===========================================
+/**
+ *（##）符号连接操作符
+ */
+///===========================================
+#define expA(s) printf("前缀加上后的字符串为:%s\n",gc_##s)  //gc_s必须存在
+
+#define expB(s) printf("前缀加上后的字符串为:%s\n",gc_  ##  s)  //gc_s必须存在
+
+#define gc_hello1 "I am gc_hello1"
+
+
+///===========================================
+/**
+ * (\)续行操作符
+ */
+///===========================================
+#define MAX(a,b) ((a)>(b) ? (a) \
+   :(b))  
+
+int main() { 
+    ///===========================================
+    /**
+     * (#)字符串操作符
+     */
+    ///===========================================
+    exp("hello");
+    exp1(hello);
+
+    string str = exp2(   bac );
+    cout<<str<<" "<<str.size()<<endl;
+    /**
+     * 忽略传入参数名前面和后面的空格。
+     */
+    string str1 = exp2( asda  bac );
+    /**
+     * 当传入参数名间存在空格时，编译器将会自动连接各个子字符串，
+     * 用每个子字符串之间以一个空格连接，忽略剩余空格。
+     */
+    cout<<str1<<" "<<str1.size()<<endl;
+
+    ///===========================================
+    /**
+     * (#)字符串操作符
+     */
+    ///===========================================
+
+    const char * gc_hello = "I am gc_hello";
+    expA(hello);
+    expB(hello1);
+
+    char var1_p[20];
+    char var2_p[20];
+
+    // 连接后的实际参数名赋值
+    strcpy(var1_p, "aaaa");
+    strcpy(var2_p, "bbbb");
+
+
+    ///===========================================
+    /**
+     * (\)续行操作符
+     */
+    ///===========================================
+    int max_val = MAX(3,6);
+    cout<<max_val<<endl;
+    return 0;
+}