一生一芯系列笔记：预学习——复习C语言

概述

本文为一生一芯系列预学习4 复习c语言的笔记，参考教程笨方法学C，因为本人有C语言基础，所以为了加快进度，本篇笔记中只完成练习0到练习18，练习32，练习33，练习42，练习44的编程算法和附加题。

练习0

总结

这个练习是关于在linux上配置环境，使用apt命令安装系统包。这个练习很简单，这里记录一下安装过程中的其他问题。
apt安装build-essential时发现我的系统的dpkg存在问题

练习1

总结

入门第一课——Hello, world！

笔记

我使用vim编辑器完成整个练习，在shell中打开vim，输入hello, world的程序，进行编译。

 ls
 vim ./ex1.c
 make ex1
cc     ex1.c   -o ex1
ex1.c: In function ‘main’:
ex1.c:3:9: warning: implicit declaration of function ‘puts’ [-Wimplicit-function-declaration]
    3 |         puts("Hello, world!");
      |         ^~~~
ex1.c:1:1: note: include ‘<stdio.h>’ or provide a declaration of ‘puts’
  +++ |+#include <stdio.h>
    1 | int main(int argc, char* argv[])

由于终端中使用了个性字符，这里的可能在某些情况下无法正常显示。在没有设置CFLAGS="-Wall"的情况下，这里出现了警告，这可能是由于环境问题。在加上#include 后，警告消失。

附加题

更改文件后应该发生error，编译失败

使用for循环多打印5行文本

#include <stdio.h>
int main(int argc, char* argv[])
{
    puts("Hello, world!");
    for(int i=0;i<5;i++){
            puts("hello");
    }
    return 0;
}

结果

阅读man 3 puts的文档

练习2

总结

make是很多大型系统的常见构建工具，大部分c/c++工程都使用make和cmake进行构建

笔记

附加题

 make ex1
make: 'ex1' is up to date.
 make clean
rm -rf ex1
 make ex1
cc ex1.c -o ex1
 cat Makefile 
CFLAGS=-Wall -g
clean:
        rm -rf ex1
ex1:
        cc ex1.c -o ex1

练习3

总结

使用printf进行格式化输出

笔记

代码运行结果

我们将printf中的age去掉后，输出如下

在printf中，由于没有指定的参数，所以printf会从栈中取一个值，这个值的位置不确定，所以我们会看到一个像随机数的数字。

附加题

为Q3添加上makefile

CFALGS=-wall -g
all: ex3
clean:
    rm -rf ./ex3
ex3:
    cc ex3.c -o ex3

练习4

总结

Valgrind是一个十分好用的程序调试工具，与gdb不同，gdb是为了更方便的观察程序的运行，而valgrind则是为了更快的告诉你程序的错误或者潜在的错误，比如变量没有初始化，内存没有释放，野指针问题等。

笔记

使用valgrind调试下面的程序

#include <stdio.h>
int main(){
    int age = 10;
    int height;
    printf("I am %d years old.\n");
    printf("I am %d inches tall.\n", height);
    return 0;
}

我们可以得到如下的输出

 valgrind ./ex3
==30798== Memcheck, a memory error detector
==30798== Copyright (C) 2002-2022, and GNU GPL'd, by Julian Seward et al.
==30798== Using Valgrind-3.19.0 and LibVEX; rerun with -h for copyright info
==30798== Command: ./ex3
==30798== 
I am -16777944 years old.
==30798== Conditional jump or move depends on uninitialised value(s)
==30798==    at 0x48CD027: __vfprintf_internal (vfprintf-process-arg.c:58)
==30798==    by 0x48C265A: printf (printf.c:33)
==30798==    by 0x109174: main (in /home/fengqi/Documents/GitRepos/ysyx/pre-study_phase/2024_12_18/Q4/ex3)
==30798== 
==30798== Use of uninitialised value of size 8
==30798==    at 0x48C1AAB: _itoa_word (_itoa.c:177)
==30798==    by 0x48CCE58: __vfprintf_internal (vfprintf-process-arg.c:164)
==30798==    by 0x48C265A: printf (printf.c:33)
==30798==    by 0x109174: main (in /home/fengqi/Documents/GitRepos/ysyx/pre-study_phase/2024_12_18/Q4/ex3)
==30798== 
==30798== Conditional jump or move depends on uninitialised value(s)
==30798==    at 0x48C1ABC: _itoa_word (_itoa.c:177)
==30798==    by 0x48CCE58: __vfprintf_internal (vfprintf-process-arg.c:164)
==30798==    by 0x48C265A: printf (printf.c:33)
==30798==    by 0x109174: main (in /home/fengqi/Documents/GitRepos/ysyx/pre-study_phase/2024_12_18/Q4/ex3)
==30798== 
==30798== Conditional jump or move depends on uninitialised value(s)
==30798==    at 0x48CD6F6: __vfprintf_internal (vfprintf-process-arg.c:174)
==30798==    by 0x48C265A: printf (printf.c:33)
==30798==    by 0x109174: main (in /home/fengqi/Documents/GitRepos/ysyx/pre-study_phase/2024_12_18/Q4/ex3)
==30798== 
I am 0 inches tall.
==30798== 
==30798== HEAP SUMMARY:
==30798==     in use at exit: 0 bytes in 0 blocks
==30798==   total heap usage: 1 allocs, 1 frees, 1,024 bytes allocated
==30798== 
==30798== All heap blocks were freed -- no leaks are possible
==30798== 
==30798== Use --track-origins=yes to see where uninitialised values come from
==30798== For lists of detected and suppressed errors, rerun with: -s
==30798== ERROR SUMMARY: 4 errors from 4 contexts (suppressed: 0 from 0)

我们可以看到valgrind指出了我们程序运行过程中访问了一些没有被初始化的地址