typedef

Why when a template class inherits from another template class, typedefs need to be respecified and functions calls qualified?

由 梦想的初衷 提交于 2020-05-23 06:13:19
问题 When a template class inherits from another template class, typedefs in the base class must be redefined again (i.e. they are not automatically inherited), and function calls in the base class need to be qualified. Why is that? Isn't this already unambiguous? So if I have 20 template classes, all defining the same typedefs, I am not able to introduce a base class containing these definitions them and inherit from it, as I have to redefine the typedefs anyway in every class, which defeats the

Why must the 'struct' keyword precede struct instances in C?

由 ≯℡__Kan透↙ 提交于 2020-05-15 05:01:08
问题 Let's say I define a struct in C. If I declare an instance of that struct, it's necessary that I include the 'struct' keyword in front of it. // Define struct struct Book { char title[50]; char author[50]; char subject[100]; int book_id; }; // Instantiate struct int main() { struct Book myBook; } My question: why is it necessary for the struct keyword to precede any instantiation of the struct? It seems like the compiler would have plenty of information to deduct that 'Book' is a struct. I

Why must the 'struct' keyword precede struct instances in C?

由 丶灬走出姿态 提交于 2020-05-15 05:00:34
问题 Let's say I define a struct in C. If I declare an instance of that struct, it's necessary that I include the 'struct' keyword in front of it. // Define struct struct Book { char title[50]; char author[50]; char subject[100]; int book_id; }; // Instantiate struct int main() { struct Book myBook; } My question: why is it necessary for the struct keyword to precede any instantiation of the struct? It seems like the compiler would have plenty of information to deduct that 'Book' is a struct. I

Typedef declaration in the form `int typedef my_int;`

由 a 夏天 提交于 2020-05-15 00:57:13
问题 To declare my_int as a type alias for int we can write: typedef int my_int; // (1) Curiously, the following also seems to define an int alias: int typedef my_int; // (2) I have never seen such syntax before. Why does it work? 回答1: My reasoning after reading C++ reference is this: (1) and (2) are declarations of the form specifiers-and-qualifiers declarators-and-initializers; with specifiers-and-qualifiers being either typedef int or int typedef . The order of specifiers and qualifiers doesn't

typedef in c: struct or function reference?

由 两盒软妹~` 提交于 2020-05-14 07:49:36
问题 Analyzing some part of software written by someone else, I found the following line of code: typedef const struct rpc_method *(*super_t)(RPC*); Ok, i know, typedef rpc_method *(*super_t)(RPC*); declares a type super_t which is a function pointer... I also know what typedef struct means, but the combination of the two?? Is it a struct with a single entry??? And what means const in this context?? Could it be that const and struct are exchanged??? Nevertheless seems to compile with my gcc eabi.

typedef in c: struct or function reference?

由 时间秒杀一切 提交于 2020-05-14 07:45:08
问题 Analyzing some part of software written by someone else, I found the following line of code: typedef const struct rpc_method *(*super_t)(RPC*); Ok, i know, typedef rpc_method *(*super_t)(RPC*); declares a type super_t which is a function pointer... I also know what typedef struct means, but the combination of the two?? Is it a struct with a single entry??? And what means const in this context?? Could it be that const and struct are exchanged??? Nevertheless seems to compile with my gcc eabi.

typedef in c: struct or function reference?

由 China☆狼群 提交于 2020-05-14 07:45:04
问题 Analyzing some part of software written by someone else, I found the following line of code: typedef const struct rpc_method *(*super_t)(RPC*); Ok, i know, typedef rpc_method *(*super_t)(RPC*); declares a type super_t which is a function pointer... I also know what typedef struct means, but the combination of the two?? Is it a struct with a single entry??? And what means const in this context?? Could it be that const and struct are exchanged??? Nevertheless seems to compile with my gcc eabi.

typedef重复定义 和 error: ‘long long long’ is too long for GCC

由 大兔子大兔子 提交于 2020-04-07 15:10:35
今天发现一个很有意思的编译问题，然后在Stack Overflow上也有看到类似的。就是出现了 long long long 类型错误提示 错误提示如下： /home/yejy/algorithm_and_data_structure/main.cpp:50:17: error: ‘long long long’ is too long for GCC #define INT64 long long ^ 顾名思义，一个long占4个字节，两个就是8字节，总共64位，等于系统是64位的，如果你使用3个long那就96位了，那肯定会有问题，正常情况下也没人会定义三个long。 ``` #define INT64 long long ``` 然后看代码出错的地方，就是一个宏定义，怎么会出现问题呢？ 然后仔细看了一下代码发现是 链接外部库 导致的，工程 A 链接了 B_lib.so 和 C_lib.so 两个动态库, 然后 B 中用宏定义了 long long ， C 中使用typedef重新命名了 long long，顺序刚好是宏定义在前，等价于下面两句代码： ``` #define INT64 long long typedef long long INT64; <p style="font-size: 15px; text-indent:2em; letter-spacing:1px

Effective Objective-C2.0读书小记（一）枚举

由 ＊爱你＆永不变心＊ 提交于 2020-04-07 11:37:40
第五条：用枚举表示状态、选项、状态码 枚举类型：enum ①枚举是一种常量命名方式。比如说： enum EOCButtonType { EOCButtonTypeCustom, EOCButtonTypeSystem, EOCButtonTypeDetailDisclosure, }; 编译器会为枚举分配一个独有的编号，从0开始，每个枚举递增+1。 当然，也可以不使用编译器分配的序号 enum EOCButtonType { EOCButtonTypeCustom=1, EOCButtonTypeSystem, EOCButtonTypeDetailDisclosure, }; 上述代码把的值设为1，而不使用编译器所分配的0，接下来的几个枚举的值都会在上一个的基础上递增1，比如说，EOCButtonTypeDetailDisclosure的值就是3. 定义枚举的方式： enum EOCButtonType type =UIButtonTypeDetailDisclosure； 用typedef关键字重新定义：（这样就不用每次定义时敲入enum而只需要写EOCButtonType了） typedef enum EOCButtonType EOCButtonType； EOCButtonType state =EOCButtonTypeDetailDisclosure；

【C语言】23-typedef

由 久未见 提交于 2020-04-07 07:32:26
一、typedef作用简介 * 我们可以使用typedef关键字为各种数据类型定义一个新名字(别名)。 1 #include <stdio.h> 2 3 typedef int Integer; 4 typedef unsigned int UInterger; 5 6 typedef float Float; 7 8 int main(int argc, const char * argv[]) { 9 Integer i = -10; 10 UInterger ui = 11; 11 12 Float f = 12.39f; 13 14 printf("%d %d %.2f", i, ui, f); 15 16 return 0; 17 } 在第3、第4、第6行分别给int、unsigned int、float起了个别名，然后在main函数中使用别名定义变量，用来跟原来的基本类型是完全一样的。输出结果： 当然，给类型起别名后，原来的int、float还是可以正常使用的： int i = 10; float f = 10.0f; * 也可以在别名的基础上再起一个别名 typedef int Integer; typedef Integer MyInteger; 二、typedef与指针 除开可以给基本数据类型起别名，typedef也可以给指针起别名 1 #include
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