小白问题:关于Cpp代码规范性 .h与.cpp文件的关系与内容的存疑

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    • #21000
      咸寒少
      参与者
        @smallsaltedfish
        楼主
        呆憨Blog
        blog.daihan.top

        最近由于更换IDE和CLI,需要将程序全部重写,于是也就考虑将之前不规范的代码整理成规范内容.

        原IDE:VEXcode Pro V5

        现IDE:PROS Editor(均为VEX机器人专用IDE)

        存疑内容:.h文件一般用于声明常量和函数 而 cpp文件一般用于表达函数逻辑.

        那我在引用.h文件时,编译器发现了声明的函数,它如何去寻找函数的逻辑内容?

        是去寻找一个cpp文件吗?要让两者关联有什么格式要求吗?

        常见.h的格式是什么样的,全局定义吗?

        为了防止重复编译还有哪些办法?除了#pragma once

      • #21001
        孙锡源
        管理员
          @ibadboy
          坏蛋的博客
          ibadboy.net

          我个人已经很多年不写C++了,以下内容只保证总体上正确:

          编译器如何寻找h文件对应的cpp文件

          这个涉及到C++编译器的编译过程:

          1. 预处理
          2. 编译
          3. 链接

          在预处理阶段,所有使用include宏标记的内容都会被原封不动的复制到当前文件中。

          比如说以下代码:

          include "hello.h"
            
          int main()
          {
                  hello();
          
                  return 0;
          }

          经过预处理后会变成这样:

          int main();
          
          int main() { 
              hello(); 
              return 0; 
          }

          可以发现,其实根本不存在所谓的“h文件与cpp文件关联”,因为h文件根本就是等于不存在,在预处理过程中它就会被全部复制到引用它的cpp中。

          关于include宏的介绍见GCC官方文档:https://gcc.gnu.org/onlinedocs/cpp/Header-Files.html

          在其后的编译过程中,每个cpp文件会被单独编译,并各自生成二进制文件。如果你没在每个cpp文件头部声明要引用的类、函数的定义,则这个阶段就会抛出函数、类未定义的错误。

          最后的链接过程可以理解成是将多个编译后的cpp文件关联成一个整体,对于在同一个命名空间和作用域中的函数、类、变量,其链接后就是全局公用的。在这个阶段如果函数的逻辑部分未发现的话g++编辑器会抛出错误。

          常见.h的格式是什么样的

          如果你的代码不包含对外提供的接口的话可以不写h文件,而是使用extern关键字声明该函数、变量、类在此cpp文件外部定义。

          当然,不怕麻烦的话给每个cpp文件写一个h文件也可以,或者也可以把多个cpp文件的定义塞到一个h文件里。

          如果有一些全局配置信息的话可以写一个类似config.h这种文件,其中只包含一些常量的定义,就好像WordPress的wp-config.php一样。

          防止重复编译

          在Linux内核中多使用以下宏来避免重复包含:

          #ifndef FOOP_H
          #define FOOP_H
          int foo(int a);
          #endif

          比如这个关于ECC加密算法的头文件:

          https://github.com/torvalds/linux/blob/master/include/crypto/ecc_curve.h

        • #21002
          咸寒少
          参与者
            @smallsaltedfish
            楼主
            呆憨Blog
            blog.daihan.top

            抱歉我还是不太懂你的意思。

            我写.h文件的目的是让给机器人下载的主函数文件尽量简洁。

            由于机器人的特殊性,我的函数要被反复反复利用。

            所以.h文件即起到函数分类的作用 也起到简洁代码的作用。

            我要是不想把逻辑写在我的主函数文件里,也不应该写在.h里面,那我应该把函数逻辑写在哪里,引用这个.h文件时,编译器才能找到它的逻辑。

            • #21003
              孙锡源
              管理员
                @ibadboy
                坏蛋的博客
                ibadboy.net

                你可以把函数逻辑写在任意cpp文件里,把函数声明写在任意h文件里(h文件和cpp文件没有任何关联关系,只要函数声明和定义能对应起来就行)

            • #21015
              咸寒少
              参与者
                @smallsaltedfish
                楼主
                呆憨Blog
                blog.daihan.top

                Adding timestamp [OK]
                Linking hot project with ./bin/cold.package.elf and libc,libm,libpros,okapilib [ERRORS]
                /usr/local/Cellar/arm-gcc-bin@10/10-2020-q4-major_1/bin/../lib/gcc/arm-none-eabi/10.2.1/../../../../arm-none-eabi/bin/ld: bin/main.cpp.o:/Users/sukanu/L3313B/./include/config.h:25: multiple definition of `LED’; bin/ctrl_func.cpp.o:/Users/sukanu/L3313B/./include/config.h:25: first defined here
                /usr/local/Cellar/arm-gcc-bin@10/10-2020-q4-major_1/bin/../lib/gcc/arm-none-eabi/10.2.1/../../../../arm-none-eabi/bin/ld: bin/main.cpp.o:/Users/sukanu/L3313B/./include/config.h:22: multiple definition of `IS’; bin/ctrl_func.cpp.o:/Users/sukanu/L3313B/./include/config.h:22: first defined here
                /usr/local/Cellar/arm-gcc-bin@10/10-2020-q4-major_1/bin/../lib/gcc/arm-none-eabi/10.2.1/../../../../arm-none-eabi/bin/ld: bin/main.cpp.o:/Users/sukanu/L3313B/./include/config.h:19: multiple definition of `RB’; bin/ctrl_func.cpp.o:/Users/sukanu/L3313B/./include/config.h:19: first defined here
                /usr/local/Cellar/arm-gcc-bin@10/10-2020-q4-major_1/bin/../lib/gcc/arm-none-eabi/10.2.1/../../../../arm-none-eabi/bin/ld: bin/main.cpp.o:/Users/sukanu/L3313B/./include/config.h:18: multiple definition of `RF’; bin/ctrl_func.cpp.o:/Users/sukanu/L3313B/./include/config.h:18: first defined here
                /usr/local/Cellar/arm-gcc-bin@10/10-2020-q4-major_1/bin/../lib/gcc/arm-none-eabi/10.2.1/../../../../arm-none-eabi/bin/ld: bin/main.cpp.o:/Users/sukanu/L3313B/./include/config.h:16: multiple definition of `ML’; bin/ctrl_func.cpp.o:/Users/sukanu/L3313B/./include/config.h:16: first defined here
                /usr/local/Cellar/arm-gcc-bin@10/10-2020-q4-major_1/bin/../lib/gcc/arm-none-eabi/10.2.1/../../../../arm-none-eabi/bin/ld: bin/main.cpp.o:/Users/sukanu/L3313B/./include/config.h:15: multiple definition of `BL’; bin/ctrl_func.cpp.o:/Users/sukanu/L3313B/./include/config.h:15: first defined here
                /usr/local/Cellar/arm-gcc-bin@10/10-2020-q4-major_1/bin/../lib/gcc/arm-none-eabi/10.2.1/../../../../arm-none-eabi/bin/ld: bin/main.cpp.o:/Users/sukanu/L3313B/./include/config.h:14: multiple definition of `FL’; bin/ctrl_func.cpp.o:/Users/sukanu/L3313B/./include/config.h:14: first defined here
                /usr/local/Cellar/arm-gcc-bin@10/10-2020-q4-major_1/bin/../lib/gcc/arm-none-eabi/10.2.1/../../../../arm-none-eabi/bin/ld: bin/main.cpp.o:/Users/sukanu/L3313B/./include/config.h:13: multiple definition of `LB’; bin/ctrl_func.cpp.o:/Users/sukanu/L3313B/./include/config.h:13: first defined here
                /usr/local/Cellar/arm-gcc-bin@10/10-2020-q4-major_1/bin/../lib/gcc/arm-none-eabi/10.2.1/../../../../arm-none-eabi/bin/ld: bin/main.cpp.o:/Users/sukanu/L3313B/./include/config.h:12: multiple definition of `LF’; bin/ctrl_func.cpp.o:/Users/sukanu/L3313B/./include/config.h:12: first defined here
                /usr/local/Cellar/arm-gcc-bin@10/10-2020-q4-major_1/bin/../lib/gcc/arm-none-eabi/10.2.1/../../../../arm-none-eabi/bin/ld: bin/main.cpp.o:/Users/sukanu/L3313B/./include/config.h:9: multiple definition of `Ctrl2′; bin/ctrl_func.cpp.o:/Users/sukanu/L3313B/./include/config.h:9: first defined here
                /usr/local/Cellar/arm-gcc-bin@10/10-2020-q4-major_1/bin/../lib/gcc/arm-none-eabi/10.2.1/../../../../arm-none-eabi/bin/ld: bin/main.cpp.o:/Users/sukanu/L3313B/./include/config.h:8: multiple definition of `Ctrl1′; bin/ctrl_func.cpp.o:/Users/sukanu/L3313B/./include/config.h:8: first defined here
                collect2: error: ld returned 1 exit status
                make: *** [bin/hot.package.elf] Error 1
                ERROR – pros.cli.build:build_compile_commands – Failed to make project: Exit Code 2
                Error: Failed to build

                 

                重复定义错误

                我重复包含了config.h文件

                做了

                #ifndef CONFIG_H
                #define CONFIG_H
                #pragma once

                的处理

                但是还是无法编译

              • #21018
                孙锡源
                管理员
                  @ibadboy
                  坏蛋的博客
                  ibadboy.net

                  代码贴上来看看。

                  记得用编辑器的插入代码功能贴,别直接复制粘贴

                • #21023
                  咸寒少
                  参与者
                    @smallsaltedfish
                    楼主
                    呆憨Blog
                    blog.daihan.top

                    config.h

                    _Pragma("once")
                    #pragma once
                    #ifndef _CONFIG_H_
                    #define _CONFIG_H_
                    
                    #include "main.h"
                    
                    //---Declare Devices---
                    //Ctrl
                    Controller Ctrl1(CONTROLLER_MASTER);
                    Controller Ctrl2(CONTROLLER_PARTNER);
                    
                    //Motor fwd
                    Motor LF(12,E_MOTOR_GEARSET_18,false);
                    Motor LB(13,E_MOTOR_GEARSET_18,false);
                    Motor FL(15,E_MOTOR_GEARSET_18,false);
                    Motor BL(16,E_MOTOR_GEARSET_18,false);
                    Motor ML(19,E_MOTOR_GEARSET_18,false);
                    //Motor rev
                    Motor RF(17,E_MOTOR_GEARSET_18,true);
                    Motor RB(18,E_MOTOR_GEARSET_18,true);
                    
                    //Imu
                    Imu IS (14);
                    
                    //3-Wire LED
                    ADIDigitalOut LED ('A');
                    
                    #endif

                    ctrl_func.h

                    #pragma once
                    #ifndef _CTRL_FUNC_H
                    #define _CTRL_FUNC_H
                    
                    #include "main.h"
                    
                    void STOP_MOVE();
                    void STOP_LIFT();
                    void LOCK();
                    void Ctrl_L(int ctrl_power);
                    
                    #endif
                    

                    ctrl_func.cpp

                    #include "main.h"
                    #include "config.h"
                    
                    long long shin_count = 0;
                    void Ctrl_Shin(bool status) {
                      shin_count++;
                      if (status) {
                        if (shin_count % 10 == 0) {
                          LED.set_value(1);
                        }
                        if (shin_count % 10 == 5) {
                          LED.set_value(0);
                        }
                      } else {
                        LED.set_value(0);
                      }
                    }
                    
                    void STOP_MOVE() {
                      LF.set_brake_mode(E_MOTOR_BRAKE_BRAKE);
                      LB.set_brake_mode(E_MOTOR_BRAKE_BRAKE);
                      RF.set_brake_mode(E_MOTOR_BRAKE_BRAKE);
                      RB.set_brake_mode(E_MOTOR_BRAKE_BRAKE);
                    }
                    
                    void STOP_LIFT() {
                      FL.set_brake_mode(E_MOTOR_BRAKE_HOLD);
                      ML.set_brake_mode(E_MOTOR_BRAKE_HOLD);
                      BL.set_brake_mode(E_MOTOR_BRAKE_HOLD);
                    }
                    
                    void LOCK() {
                      STOP_MOVE();
                      STOP_LIFT();
                    }
                    
                    void Ctrl_L(int ctrl_power) {
                      if (ctrl_power == 0) {
                        LF.set_brake_mode(E_MOTOR_BRAKE_BRAKE);
                        LB.set_brake_mode(E_MOTOR_BRAKE_BRAKE);
                      } else {
                        LF.move(ctrl_power);
                        LB.move(ctrl_power);
                      }
                    }
                    

                    main.cpp

                    #include "main.h"
                    #include "config.h"
                    #include "ctrl_func.h"
                    
                    /**
                     * Runs initialization code. This occurs as soon as the program is started.
                     *
                     * All other competition modes are blocked by initialize; it is recommended
                     * to keep execution time for this mode under a few seconds.
                     */
                    void initialize() {
                           LED.set_value(1);
                           LF.set_zero_position(0);
                      LB.set_zero_position(0);
                      RF.set_zero_position(0);
                      RB.set_zero_position(0);
                      FL.set_zero_position(0);
                      BL.set_zero_position(0);
                      ML.set_zero_position(0);
                      IS.reset();
                           LED.set_value(0);
                    }
                    
                    /**
                     * Runs while the robot is in the disabled state of Field Management System or
                     * the VEX Competition Switch, following either autonomous or opcontrol. When
                     * the robot is enabled, this task will exit.
                     */
                    void disabled() {
                           LOCK();
                    }
                    
                    /**
                     * Runs after initialize(), and before autonomous when connected to the Field
                     * Management System or the VEX Competition Switch. This is intended for
                     * competition-specific initialization routines, such as an autonomous selector
                     * on the LCD.
                     *
                     * This task will exit when the robot is enabled and autonomous or opcontrol
                     * starts.
                     */
                    void competition_initialize() {}
                    
                    /**
                     * Runs the user autonomous code. This function will be started in its own task
                     * with the default priority and stack size whenever the robot is enabled via
                     * the Field Management System or the VEX Competition Switch in the autonomous
                     * mode. Alternatively, this function may be called in initialize or opcontrol
                     * for non-competition testing purposes.
                     *
                     * If the robot is disabled or communications is lost, the autonomous task
                     * will be stopped. Re-enabling the robot will restart the task, not re-start it
                     * from where it left off.
                     */
                    void autonomous() {}
                    
                    /**
                     * Runs the operator control code. This function will be started in its own task
                     * with the default priority and stack size whenever the robot is enabled via
                     * the Field Management System or the VEX Competition Switch in the operator
                     * control mode.
                     *
                     * If no competition control is connected, this function will run immediately
                     * following initialize().
                     *
                     * If the robot is disabled or communications is lost, the
                     * operator control task will be stopped. Re-enabling the robot will restart the
                     * task, not resume it from where it left off.
                     */
                    void opcontrol() {
                           Controller master(E_CONTROLLER_MASTER);
                           Motor left_mtr(1);
                           Motor right_mtr(2);
                    
                           while (true) {
                                  lcd::print(0, "%d %d %d", (lcd::read_buttons() & LCD_BTN_LEFT) >> 2,
                                                   (lcd::read_buttons() & LCD_BTN_CENTER) >> 1,
                                                   (lcd::read_buttons() & LCD_BTN_RIGHT) >> 0);
                                  int left = master.get_analog(ANALOG_LEFT_Y);
                                  int right = master.get_analog(ANALOG_RIGHT_Y);
                    
                                  left_mtr = left;
                                  right_mtr = right;
                                  delay(10);
                           }
                    }
                    

                    main.h

                    /**
                     * file main.h
                     *
                     * Contains common definitions and header files used throughout your PROS
                     * project.
                     *
                     * Copyright (c) 2017-2021, Purdue University ACM SIGBots.
                     * All rights reserved.
                     *
                     * This Source Code Form is subject to the terms of the Mozilla Public
                     * License, v. 2.0. If a copy of the MPL was not distributed with this
                     * file, You can obtain one at http://mozilla.org/MPL/2.0/.
                     */
                    
                    #ifndef _PROS_MAIN_H_
                    #define _PROS_MAIN_H_
                    
                    /**
                     * If defined, some commonly used enums will have preprocessor macros which give
                     * a shorter, more convenient naming pattern. If this isn't desired, simply
                     * comment the following line out.
                     *
                     * For instance, E_CONTROLLER_MASTER has a shorter name: CONTROLLER_MASTER.
                     * E_CONTROLLER_MASTER is pedantically correct within the PROS styleguide, but
                     * not convienent for most student programmers.
                     */
                    #define PROS_USE_SIMPLE_NAMES
                    
                    /**
                     * If defined, C++ literals will be available for use. All literals are in the
                     * pros::literals namespace.
                     *
                     * For instance, you can do 4_mtr = 50 to set motor 4's target velocity to 50
                     */
                    #define PROS_USE_LITERALS
                    
                    #include "api.h"
                    #include <bits/stdc++.h>//Added by Sukanu
                    
                    /**
                     * You should add more #includes here
                     */
                    //#include "okapi/api.hpp"
                    //#include "pros/api_legacy.h"
                    
                    /**
                     * If you find doing pros::Motor() to be tedious and you'd prefer just to do
                     * Motor, you can use the namespace with the following commented out line.
                     *
                     * IMPORTANT: Only the okapi or pros namespace may be used, not both
                     * concurrently! The okapi namespace will export all symbols inside the pros
                     * namespace.
                     */
                    using namespace pros;
                    using namespace std;//Added by Sukanu
                    // using namespace pros::literals;
                    // using namespace okapi;
                    
                    /**
                     * Prototypes for the competition control tasks are redefined here to ensure
                     * that they can be called from user code (i.e. calling autonomous from a
                     * button press in opcontrol() for testing purposes).
                     */
                    #ifdef __cplusplus
                    extern "C" {
                    #endif
                    void autonomous(void);
                    void initialize(void);
                    void disabled(void);
                    void competition_initialize(void);
                    void opcontrol(void);
                    #ifdef __cplusplus
                    }
                    #endif
                    
                    #ifdef __cplusplus
                    /**
                     * You can add C++-only headers here
                     */
                    #include <iostream>
                    #endif
                    
                    #endif  // _PROS_MAIN_H_
                    

                     

                  • #21025
                    孙锡源
                    管理员
                      @ibadboy
                      坏蛋的博客
                      ibadboy.net

                      先把代码改成最简版本。就只留下config.h引入相关的代码,然后config.h里面只留下一个常量,去掉其他所有注释和无关代码。目前这一大摊把我眼睛看瞎了,尤其是你这代码依赖特定环境,又不能在本地调试。

                      另外,在其他.h里面引入main.h是什么操作?

                      最后你的项目目录是/Users/sukanu/L3313B?

                      • #21029
                        咸寒少
                        参与者
                          @smallsaltedfish
                          楼主
                          呆憨Blog
                          blog.daihan.top

                          在其他.h中引入main.h是因为其他.h的定义也需要main.h中机器人函数库的支持。

                          我的项目目录没错,就是这个。

                          我怀疑是不是因为我同时在main.cpp和ctrl_func.cpp都引用了config.h导致不同文件无法只编译一次。

                          这个问题怎么破?

                          • #21030
                            孙锡源
                            管理员
                              @ibadboy
                              坏蛋的博客
                              ibadboy.net

                              先把代码精简成最小demo,见我前面的回复。

                              排错得先移除干扰因素

                              • #21042
                                咸寒少
                                参与者
                                  @smallsaltedfish
                                  楼主
                                  呆憨Blog
                                  blog.daihan.top

                                  已经自行排查 找到原因

                                  Cpp的仅编译一次似乎是针对单一文件的

                                  一旦我建立两个cpp源文件 好像就必定编译config.h两次

                                  由于机器人的设备定义是依赖现有机器人CLI来实现的

                                  导致重复定义必报错

                                  这好像是无解的.

                                • #21045
                                  孙锡源
                                  管理员
                                    @ibadboy
                                    坏蛋的博客
                                    ibadboy.net

                                    确实是只能单个文件,其针对的是循环依赖的场景。因为预处理阶段是针对每个.cpp文件单独进行的,所以对于多个cpp文件会失效。

                                    对于全局变量,你可以这样处理:

                                    只在main.cpp中包含config.h,然后在其他cpp文件中使用extern关键字来标识要访问的变量,这样就可以了。

                                     

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