1.1 Linux directory and file commands:#

cat/tail/head, less/more, nano/vim, file, whereis, echo

You can click here to visit the commands of Linux/Ubuntu

cd /mnt/d

cd /root/

cd /

cd ~

rm test.txt hello

cp main.cpp test

mv A B

mv A B C

1.2 lists of commands, pipelines#

2.1 compile multiple files#

You can compile the files one by one and then link them to an executable file.

Another choice is using one step to list all the .c(or .cpp) files after gcc(or g++) command and create an executable file named a.out.

//area.h
#define PI 3.1415

double compute_area(double r);

//area.c
#include "area.h"

double compute_area(double r)
{
    return PI * r * r;
}

//main.c
#include <stdio.h>
#include "area.h"

int main()
{
    double r, area;

    printf("Please input a radius:");
    scanf("%lf", &r);

    area = compute_area(r);

    printf("The area of %lf is %.4lf\n", r, area);

    return 0;
}

3.1 Define Macros/Variables in the makefile#

To improve the efficiency of the makefile, we use variables.

start withWrite target, prerequisite and commands by variables using $()

NOTE

Deletes all the .o files and executable file created previously before using make command. Otherwise, it’ll display:

If only one source file is modified, we need not compile all the files. So, let’s modify the makefile.

If main.cpp is modified, it is compiled by make.

All the .cpp files are compiled to the .o files, so we can modify the makefile like this:

# Using several ruls and several targes
CXX = g++
TARGET = testfiles
0BJ = main.o printinfo.o factorial.o

# options pass to the compilen
#-c generates the object file
# -Wall displays compiler warning
CFLAGS = -c -Wall

$(TARGET) : $(OBJ)
	$(CXX) -o $@ $(OBJ)

%.o : %.cpp
	$(CXX) $(CFLAGS) $^

$@: the target file

$^: all the prerequisites files

$<: the first prerequisite file

%.o:%.cpp

or

$(CXX) $(CFLAGES)$^

TIP

实际上，就是说Makefile的存在很好的消除了我们的命令行输入输出需求。正所谓前人栽树后人乘凉的道理，由于VSCode本身不存在已经配置好的环境，我们还需要自己手动写一份Makefile文件【当然也可以用ai作为助手当作辅佐工具】，如果实在是头疼配置问题，可以移步到下载VS(Visual Studio)的下载，VSCode只是相当于一个轻文本编辑器，许多环境都是我们自行配置的，而VS相当于集成的IDE，只是所需内存更大。但是相对而言，VS的即装即用是很多学C/Cpp的新手首选。

3.2 Phony target#

Using phony target to clean up compiled results automatically

# Using several rules and several targets

CXX = g++
TARGET = testfiles
OBJ = main.o printinfo.o factorial.o

# options pass to the compiler
# -c generates the object file
# -Wall displays compiler warning
CFLAGS = -c -Wall

$(TARGET) : $(OBJ)
	$(CXX) -o $@ $(OBJ)

%.o : %.cpp
	$(CXX) $(CFLAGS) $^

.PHONY : clean
clean:
	rm -f *.o $(TARGET)

Because clean is a label not a target, the command make clean can execute the clean part. Only make command can not execute clean part.

Adding .PHONY to a target will prevent making from confusing the phony target with a file name.

TIP

这里实际上就是借用了PHONY来删除多余的编译文件

Functions in makefile

SRC=$(wildcard ./*.cpp)$
target:
	@echo $(SRC)$

patsubst(pattern substitution): replace file

$(patsubst original pattern, target pattern, file list)

SRC = $(wildcard ./*.cpp)$
OBJ = $(pasubst %.cpp,%o,$(SRC))$
target:
	@echo $(SRC)
	@echo $(OBJ)

3.3 OBJS vs OBJ#

OBJS=$(patsubst %.cpp,%.o,$(SRC))$

Vs

OBJ=main.o printinfo.o factorial.o

TIP

我们可以看到OBJS只需要描述法就可以使用了，比OBJ直接列举法要来得简单得多。但是利弊也是看情况，文件不多的情况下也可以酌情用OBJ。

3.4 Use Options to Control Optimization#

-O1, the compiler tries to reduce code size and execution time, without performing any optimizations that take a great deal of compilation time.

-O2,Optimize even more. GCC performs nearly all supported optimizations that do not involve a space-speed tradeoff. As compared to -O1, this option increases both compilation time and the performance of the generated code.

-O3, Optimize yet more. O3 turns on all optimizations specified by -O2.

You can click here to learn more:

Options from org

Optional details from csdn

GNU Make Manual

4.1 Exercises . commands and command list#

The existing directory structure is shown in the upper right image. There are different types of C/C++files in the p1 directory while the directory structure under p2 is unknown.

WARNING

Task. Use the command list to create subdirectories as needed and place files of different types into different subdirectories in the p2 directory (as shown in the lower right image).Place the header file in p2/inc, and the cpp source file in p2/src, and create p2/build.

NOTE

1. when using commands, if there is already an inc subdirectories, do not create inc repeatly. If there is no inc subdirectories, create it;The same requirement also applies to src and build.

2. File copying work should only be performed after the destination subdirectories have been created.

3. Use as few command lists as possible to complete this exercise (options include and list, or list, command sequence, which can be combined as needed)

My implements:

or use this:

mkdir -p p2 &&
cd p2 &&
mkdir -p inc src build && \
cp -u ../lab/functions.h inc/ && \
cp -u ../lab/makefile inc/ && \
cp -u ../lab/factorial.cpp src/ && \
cp -u ../lab/main.cpp src/ && \
cp -u ../lab/printhello.cpp src/

4.2 Exercises . Makefile and make#

create a makefile, run it by command make or make clean to complete following tasks:

1. compile your project(program) or only compile the update files in the project by running makebased on makefile to generate the executable file lab3_practice.

   NOTE

   the object file *.o and the executable file lab3_practice should be in the directory build

   TIP

   根据这个目录去放置并且自行撰写Makefile文件

   # 定义编译器
   CC=g++
   # 定义编译选项
   CFLAGS=-Wall -g -IInc
   # 定义目标文件目录
   BUILD_DIR=build
   # 定义源文件目录
   SRC_DIR=src
   # 定义头文件目录
   INC_DIR=Inc
   # 定义源文件
   SRCS=$(wildcard $(SRC_DIR)/*.cpp)
   # 定义目标文件
   OBJS=$(patsubst $(SRC_DIR)/%.cpp,$(BUILD_DIR)/%.o,$(SRCS))
   # 定义最终的可执行文件
   TARGET=$(BUILD_DIR)/lab3_practice
   
   # 创建目标文件目录
   $(BUILD_DIR):
   	mkdir -p $(BUILD_DIR)
   
   # 编译目标文件
   $(BUILD_DIR)/%.o: $(SRC_DIR)/%.cpp | $(BUILD_DIR)
   	$(CC) $(CFLAGS) -c $< -o $@
   
   # 链接目标文件生成可执行文件
   $(TARGET): $(OBJS)
   	$(CC) $(OBJS) -o $@

2. remove all the files in the directory build by running make clean

   # 清理生成的文件
   clean:
       rm -rf $(BUILD_DIR)

3. edit the source file lab3_practice.cpp (change parameter 5 to another number), save it, then run make again, which object file would be updated in the process?

   由于fib文件有错，修改factorial为fib，否则会没有定义fib而编译失败。

   #include "functions.h"
   
   int fib(int n) {
       if (n <= 1) return n;
       return fib(n - 1) + fib(n - 2);
   }

   

4.3 Exercises . Run the following source code and explain the result.#

You need to explain the reason to a SA to pass the test.

#include <iostream>
using namespace std;

int main()
{
    for(size_t n = 2; n >= 0; n--)
        cout << "n = " << n << "  "; 

    return 0;
    
}

Using the size_t,and the size_t, and the range of the type like the unsigned int ， so you will konw the n will not be less than 0.

4.4 Exerices . Run the following source code and explain the result.#

You need to explain the reason to a SA to pass the test.

#include <iostream>
using namespace std;

int main()
{
    int n = 5;
    int sum;
    while(n >0){
        sum += n;
        cout << "n = " << n << "  ";
        cout << "sum = " << sum << "  ";
    }
    return 0;
}

Firstly,the code shows us a while-loop when n>0 its condition is true,but the sum donot initialize and n donot plus or mins to the while-loop is ALWAYS-TRUE.

#include <iostream>
using namespace std;

int main()
{
    unsigned int n = 5;  
    int sum;
    while(n >0){
        sum += n;
        cout << "n = " << (n-=2) <<endl;
        cout << "sum = " << sum << "  ";
    }
    return 0;
}

Secondly,the code shows the n is the unsigned int type ,but the sum still donot initialize.Then the n still not plus or mins to the while-loop is ALWAYS-TRUE .

Thirdly, there’re the same question in the two Codes,just like sum donot initialize and the n donot changes. So we should make the n mins,and initialize the sum.

4.5 Exerices. Run the following source code and explain the result.#

#include <iostream>
using namespace std;

int main()
{
    int n,fa;

    do{
        fa *= n;
        n++;
    }while(n <= 10);

    cout << "fa = " << fa << endl;

    return 0;
}

Actually, there’re the same problems in the Exerices4.4,donot initialize the participation elements of while-loop, it will effect on the while-loop cannot excute rightly.