Linux C 标准程序设计【语法规范篇】

#include <stdio.h>

/*
  块注释
*/
int main(int argc, char *argv[]) {
    printf("hello world!\n");      // 行注释
    return 0;
}

sudo apt-get install build-essential

gcc [-options] [filename]

➜  gcc main.c
➜  ls
a.out  main.c

➜  ./a.out
hello world!

➜  gcc main.c -o main
➜  ls
main  main.c

➜  ./main
hello world!

➜  gcc -v main.c
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/7/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu 7.3.0-27ubuntu1~18.04' --with-bugurl=file:///usr/share/doc/gcc-7/README.Bugs --enable-languages=c,ada,c++,go,brig,d,fortran,objc,obj-c++ --prefix=/usr --with-gcc-major-version-only --program-suffix=-7 --program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --with-default-libstdcxx-abi=new --enable-gnu-unique-object --disable-vtable-verify --enable-libmpx --enable-plugin --enable-default-pie --with-system-zlib --with-target-system-zlib --enable-objc-gc=auto --enable-multiarch --disable-werror --with-arch-32=i686 --with-abi=m64 --with-multilib-list=m32,m64,mx32 --enable-multilib --with-tune=generic --enable-offload-targets=nvptx-none --without-cuda-driver --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 7.3.0 (Ubuntu 7.3.0-27ubuntu1~18.04)
COLLECT_GCC_OPTIONS='-v' '-mtune=generic' '-march=x86-64'
 /usr/lib/gcc/x86_64-linux-gnu/7/cc1 -quiet -v -imultiarch x86_64-linux-gnu main.c -quiet -dumpbase main.c -mtune=generic -march=x86-64 -auxbase main -version -fstack-protector-strong -Wformat -Wformat-security -o /tmp/cc9yluga.s
GNU C11 (Ubuntu 7.3.0-27ubuntu1~18.04) version 7.3.0 (x86_64-linux-gnu)
	compiled by GNU C version 7.3.0, GMP version 6.1.2, MPFR version 4.0.1, MPC version 1.1.0, isl version isl-0.19-GMP
... ...

➜  gcc -os main.c -o main
➜  ll
总用量 16K
-rwxrwxr-x 1 hank hank 8.2K 2月  24 17:51 main
-rw-rw-r-- 1 hank hank  136 2月  21 18:12 main.c

➜  gcc main.c
➜  ll
-rwxrwxr-x 1 hank hank 8.2K 2月  24 17:58 a.out

➜  gcc -g main.c
➜  ll
-rwxrwxr-x 1 hank hank 11K 2月  24 17:58 a.out

➜  gcc -v main.c -I /workspace
#include "..." search starts here:
#include <...> search starts here:
 /workspace
 /usr/lib/gcc/x86_64-linux-gnu/7/include
 /usr/local/include
 /usr/lib/gcc/x86_64-linux-gnu/7/include-fixed
 /usr/include/x86_64-linux-gnu
 /usr/include

➜  gcc -E main.c -o main.i
➜  ls
main.c  main.i

➜  gcc -S main.i
➜  ls
main.c  main.i  main.s

➜  gcc -c main.s
➜  ls
main.c  main.i  main.s  main.o

➜  gcc main.o -o main
➜  ls
main.c  main.i  main.o  main.s  main

➜  gcc main.c
➜  ll
总用量 16K
-rwxrwxr-x 1 hank hank 8.2K 2月  22 18:25 a.out
-rw-rw-r-- 1 hank hank  136 2月  21 18:12 main.c

➜  gcc main.c -static
➜  ll
总用量 832K
-rwxrwxr-x 1 hank hank 825K 2月  22 18:25 a.out
-rw-rw-r-- 1 hank hank  136 2月  21 18:12 main.c

➜  ls
func1.c  func2.c  main.c

➜  gcc -c func1.c func2.c
➜  ls
func1.c  func1.o  func2.c  func2.o  main.c

➜  ar -r libmain.a func1.o func2.o
ar: 正在创建 libmain.a
➜  ll
总用量 36K
-rw-rw-r-- 1 hank hank   84 2月  24 20:06 func1.c
-rw-rw-r-- 1 hank hank 1.6K 2月  24 20:16 func1.o
-rw-rw-r-- 1 hank hank   84 2月  24 20:16 func2.c
-rw-rw-r-- 1 hank hank 1.6K 2月  24 20:16 func2.o
-rw-rw-r-- 1 hank hank 3.3K 2月  24 20:16 libmain.a
-rw-rw-r-- 1 hank hank  136 2月  21 18:12 main.c

➜  ls
func1.c  func2.c  main.c

➜  gcc -c -fpic func1.c func2.c
➜  ls
func1.c  func1.o  func2.c  func2.o  main.c

➜  gcc -shared func1.o func2.o -o libmain.so
➜  ll
总用量 28K
-rw-rw-r-- 1 hank hank   84 2月  24 20:06 func1.c
-rw-rw-r-- 1 hank hank 1.6K 2月  24 21:31 func1.o
-rw-rw-r-- 1 hank hank   84 2月  24 20:16 func2.c
-rw-rw-r-- 1 hank hank 1.6K 2月  24 21:31 func2.o
-rwxrwxr-x 1 hank hank 7.8K 2月  24 21:32 libmain.so
-rw-rw-r-- 1 hank hank  136 2月  21 18:12 main.c

➜  ls
func1.c  func2.c  main.c
➜  gcc -fpic -shared func1.c func2.c -o libmain.so
➜  ls
func1.c  func2.c  main.c  libmain.so

➜  gcc main.c -std=c90

main.c: In function ‘main’:
main.c:7:36: error: C++ style comments are not allowed in ISO C90
     printf("hello world!\n");      // 行注释
                                    ^
main.c:7:36: error: (this will be reported only once per input file)

➜  gdb

GNU gdb (Ubuntu 8.1-0ubuntu3) 8.1.0.20180409-git
Copyright (C) 2018 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-linux-gnu".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
<http://www.gnu.org/software/gdb/documentation/>.
For help, type "help".
Type "apropos word" to search for commands related to "word".
(gdb) |

(gdb) help
List of classes of commands:

aliases -- Aliases of other commands
breakpoints -- Making program stop at certain points
data -- Examining data
files -- Specifying and examining files
internals -- Maintenance commands
obscure -- Obscure features
running -- Running the program
stack -- Examining the stack
status -- Status inquiries
support -- Support facilities
tracepoints -- Tracing of program execution without stopping the program
user-defined -- User-defined commands

Type "help" followed by a class name for a list of commands in that class.
Type "help all" for the list of all commands.
Type "help" followed by command name for full documentation.
Type "apropos word" to search for commands related to "word".
Command name abbreviations are allowed if unambiguous.

#include <stdio.h>

int main(int argc, char *argv[]) {
  printf("当前执行程序的名称：%s\n", argv[0]);
  int index;
  for (index = 1; index < argc; index++) {
    printf("执行命令时输入的第%d个参数为：%s\n", index, argv[index]);
  }
  return 0;
}

➜  gcc -g main.c
➜  ls
a.out  main.c

➜  gdb
... ...
(gdb) file a.out
Reading symbols from a.out...done.

(gdb) run 这是一个Hank的测试程序！
Starting program: /workspace/c-test/a.out 这是一个Hank的测试程序！
当前执行程序的名称：/workspace/c-test/a.out
执行命令时输入的第1个参数为：这是一个Hank的测试程序！
[Inferior 1 (process 7997) exited normally]

(gdb) where
No stack.

(gdb) list
1 #include <stdio.h>
2
3 int main(int argc, char *argv[]) {
4   printf("当前执行程序的名称：%s\n", argv[0]);
5   int index;
6   for (index = 1; index < argc; index++) {
7     printf("执行命令时输入的第%d个参数为：%s\n", index, argv[index]);
8   }
9   return 0;
10 }(gdb)

(gdb) break 5
Breakpoint 1 at 0x555555554674: file main.c, line 5.

(gdb) run
Starting program: /workspace/c-test/a.out 这是一个Hank的测试程序！
当前执行程序的名称：/workspace/c-test/a.out

Breakpoint 1, main (argc=2, argv=0x7fffffffded8) at main.c:6
6   for (index = 1; index < argc; index++) {

(gdb) next
7     printf("执行命令时输入的第%d个参数为：%s\n", index, argv[index]);
(gdb) next
执行命令时输入的第1个参数为：这是一个Hank的测试程序！
6   for (index = 1; index < argc; index++) {

(gdb) print index
$1 = 1
(gdb) print argc
$2 = 2
(gdb) print argv
$3 = (char **) 0x7fffffffded8

(gdb) kill
Kill the program being debugged? (y or n) y
(gdb) quit

   ┌──main.c───────────────────────────────────────────────────────────────────┐
   │1       #include <stdio.h>                                                 │
   │2                                                                          │
   │3       int main(int argc, char *argv[]) {                                 │
   │4         printf("当前执行程序的名称：%s\n", argv[0]);                       │
   │5         int index;                                                       │
   │6         for (index = 1; index < argc; index++) {                         │
   │7           printf("执行命令时输入的第%d个参数为：%s\n", index, argv[index]); │
   │8         }                                                                │
   │9         return 0;                                                        │
   │10      }^?                                                                │
   │11                                                                         │
   │12                                                                         │
   │13                                                                         │
   │14                                                                         │
   └───────────────────────────────────────────────────────────────────────────┘
exec No process In:                                                L??   PC: ??
Find the GDB manual and other documentation resources online at:
<http://www.gnu.org/software/gdb/documentation/>.
For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from a.out...done.
---Type <return> to continue, or q <return> to quit---2 in /workspace/c-test/main.c
(gdb) |

sudo apt-get install ddd

int date = 2019;

const int USER = "Hank";

#include <stdio.h>

int main()
{
  printf("int %ld byte\n", sizeof(int));                               // int 4 byte
  printf("unsigned int %ld byte\n", sizeof(unsigned int));             // unsigned int 4 byte
  printf("short %ld byte\n", sizeof(short));                           // short 2 byte
  printf("unsigned short %ld byte\n", sizeof(unsigned short));         // unsigned short 2 byte
  printf("long %ld byte\n", sizeof(long));                             // long 8 byte
  printf("unsigned long %ld byte\n", sizeof(unsigned long));           // unsigned long 8 byte
  printf("long long %ld byte\n", sizeof(long long));                   // long long 8 byte
  printf("unsigned long long %ld byte\n", sizeof(unsigned long long)); // unsigned long long 8 byte
  return 0;
}

#include <stdio.h>

int main() {
    int birthday= -1988;
    printf("%d\n", birthday);  // -1988
    printf("%u\n", birthday);  // 4294965308
    return 0;
}

#include <stdio.h>

int main()
{
  printf("char %ld byte\n", sizeof(char));                   // char 1 byte
  printf("unsigned char %ld byte\n", sizeof(unsigned char)); // unsigned char 1 byte
  return 0;
}

#include <stdio.h>

int main() {
    char test= 'h';
    printf("%d\n", test);  // 104
    printf("%c\n", test);  // h
    return 0;
}

#include <stdio.h>

int main() {
    char test = 255; // GCC默认字符型变量为有符号类型
    printf("%c \n", test);  // �
    printf("%d \n", test);  // -1
    return 0;
}

int main() {
    unsigned char test = 255; // 显式声明字符型变量为无符号类型
    printf("%c \n", test);  // �
    printf("%d \n", test);  // 255
    return 0;
}

#include <stdio.h>

int main() {
    float pi_f = 3.14;
    double pi_b = 3.14;
    long double pi_ld = 3.14;

    printf("float %ld byte\n", sizeof(pi_f));         // float 4 byte
    printf("double int %ld byte\n", sizeof(pi_b));    // double int 8 byte
    printf("long double %ld byte\n", sizeof(pi_ld));  // long double 16 byte

    return 0;
}

#include <stdio.h>

int main() {
    float i  = 3.14159;
    /* 打印一个变量占用的空间 */
    printf("float is %d byte\n", sizeof(i));        // float is 4 byte
    /* 打印一个常量占用的空间 */
    printf("double is %d byte\n", sizeof(3.14159)); // double is 8 byte

    return 0;
}

#include <stdio.h>

int main() {
    int i  = 5;
    float f = 3.14;
    char c = 'H';

    printf("result have %ld byte\n", sizeof(i+f)); // result have 4 byte
    printf("result have %ld byte\n", sizeof(c+f)); // result have 4 byte

    return 0;
}

#include <stdio.h>

int main() {
    char i  = 'A';
    printf("result still have %ld byte\n", sizeof((float)i)); // result still have 4 byte
    return 0;44
}

#include <stdio.h>
#define true 1
#define false 0

typedef int bool;

void main() {
  bool test = false;
  if (test != true) {
    printf("工作情况良好！\n");
  }
}

#include <stdio.h>

void main()
{
  _Bool true = 0;
  _Bool false = 1;
  printf("_Bool is %ld byte\n", sizeof(_Bool)); // _Bool is 1 byte
}

#include <stdio.h>
#include <stdbool.h>

int main(void) {
  bool truly = true;
  bool falsely = false;
  printf("true is %d and false is %d.\n", truly, falsely); // true is 1 and false is 0.
  return 0;
}

#include <stdio.h>
#include <stdbool.h>
#include <stdlib.h>

int main(void)
{
  bool year = 1985;
  printf("Ops, year equals %d!\n", year); // Ops, year equals 1!
  return EXIT_SUCCESS;
}

/* 声明Date结构体类型 */
struct Date {
  int year;
  int month;
  int day;
}

/* 声明Student结构体类型 */
struct Student {
  int age;
  char name[10];
  char address[20];
  struct Date birthday; // 声明Date结构体变量
}

struct Student hank; // 声明Student结构体变量

union Variable {
  char character;  // 有符号字符型，占用1个字节空间。
  int integer;     // 基本整型，占用2个字节空间。
  float real;      // 单精度浮点型，占用4个字节空间。
}

Variable.integer = 100; // 将整数100存储在Variable结构体变量。