一起来学C语言吧 - 1

C语言编辑器我用的是CLion，有点狮子、勇猛的人的意思-lion。也是这个杀手不太冷的lion-里昂。

希望这个专栏能像伴随着你的狮子和这个不太冷的杀手一样，给你带来帮助和底气、勇气。

先看个简单的吧：

#include <stdio.h>
//输出
int main()
{
    printf("23+43=%d\n",23+43);

    return 0;
}

如果你找到java或者python，这个main就类似java的main方法以及python的if name == 'main':
java main:

public static void main(String[] args){
	System.out.println("Hello World");
}

python main:

def doors(n):
    return int(n**.5)
    # return sum([1 for i in range(1, n + 1) if (i ** 0.5).is_integer()])
if __name__ == '__main__':
    result = doors(8)
    print('result %s' % result)

就是表明这个方法可以在编辑器直接执行，并占据主线程。
题外话 前几天看朋友圈别人分享的《西蒙学习法》，其实一个人学不同的技术、甚至不同的技术领域、不同的专业领域的事情，把每一件掌握得很好、深入其实是件非常难和难以掌握的事情。

除了main，在C语言的“导包”中，使用的是include关键字，
让我点开这个<stdio.h>看下：

/*
 * Copyright (c) 2000, 2005, 2007, 2009, 2010 Apple Inc. All rights reserved.
 *
 * @APPLE_LICENSE_HEADER_START@
 *
 * This file contains Original Code and/or Modifications of Original Code
 * as defined in and that are subject to the Apple Public Source License
 * Version 2.0 (the 'License'). You may not use this file except in
 * compliance with the License. Please obtain a copy of the License at
 * http://www.opensource.apple.com/apsl/ and read it before using this
 * file.
 *
 * The Original Code and all software distributed under the License are
 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
 * Please see the License for the specific language governing rights and
 * limitations under the License.
 *
 * @APPLE_LICENSE_HEADER_END@
 */
/*-
 * Copyright (c) 1990, 1993
 *	The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Chris Torek.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *	This product includes software developed by the University of
 *	California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *	@(#)stdio.h	8.5 (Berkeley) 4/29/95
 */

#ifndef	_STDIO_H_
#define	_STDIO_H_

#include <_stdio.h>

__BEGIN_DECLS
extern FILE *__stdinp;
extern FILE *__stdoutp;
extern FILE *__stderrp;
__END_DECLS

#define	__SLBF	0x0001		/* line buffered */
#define	__SNBF	0x0002		/* unbuffered */
#define	__SRD	0x0004		/* OK to read */
#define	__SWR	0x0008		/* OK to write */
	/* RD and WR are never simultaneously asserted */
#define	__SRW	0x0010		/* open for reading & writing */
#define	__SEOF	0x0020		/* found EOF */
#define	__SERR	0x0040		/* found error */
#define	__SMBF	0x0080		/* _buf is from malloc */
#define	__SAPP	0x0100		/* fdopen()ed in append mode */
#define	__SSTR	0x0200		/* this is an sprintf/snprintf string */
#define	__SOPT	0x0400		/* do fseek() optimisation */
#define	__SNPT	0x0800		/* do not do fseek() optimisation */
#define	__SOFF	0x1000		/* set iff _offset is in fact correct */
#define	__SMOD	0x2000		/* true => fgetln modified _p text */
#define __SALC  0x4000		/* allocate string space dynamically */
#define __SIGN  0x8000		/* ignore this file in _fwalk */

/*
 * The following three definitions are for ANSI C, which took them
 * from System V, which brilliantly took internal interface macros and
 * made them official arguments to setvbuf(), without renaming them.
 * Hence, these ugly _IOxxx names are *supposed* to appear in user code.
 *
 * Although numbered as their counterparts above, the implementation
 * does not rely on this.
 */
#define	_IOFBF	0		/* setvbuf should set fully buffered */
#define	_IOLBF	1		/* setvbuf should set line buffered */
#define	_IONBF	2		/* setvbuf should set unbuffered */

#define	BUFSIZ	1024		/* size of buffer used by setbuf */
#define	EOF	(-1)

				/* must be == _POSIX_STREAM_MAX <limits.h> */
#define	FOPEN_MAX	20	/* must be <= OPEN_MAX <sys/syslimits.h> */
#define	FILENAME_MAX	1024	/* must be <= PATH_MAX <sys/syslimits.h> */

/* System V/ANSI C; this is the wrong way to do this, do *not* use these. */
#ifndef _ANSI_SOURCE
#define	P_tmpdir	"/var/tmp/"
#endif
#define	L_tmpnam	1024	/* XXX must be == PATH_MAX */
#define	TMP_MAX		308915776

#ifndef SEEK_SET
#define	SEEK_SET	0	/* set file offset to offset */
#endif
#ifndef SEEK_CUR
#define	SEEK_CUR	1	/* set file offset to current plus offset */
#endif
#ifndef SEEK_END
#define	SEEK_END	2	/* set file offset to EOF plus offset */
#endif

#define	stdin	__stdinp
#define	stdout	__stdoutp
#define	stderr	__stderrp

#ifdef _DARWIN_UNLIMITED_STREAMS
#if defined(__IPHONE_OS_VERSION_MIN_REQUIRED) && __IPHONE_OS_VERSION_MIN_REQUIRED < __IPHONE_3_2
#error "_DARWIN_UNLIMITED_STREAMS specified, but -miphoneos-version-min version does not support it."
#elif defined(__MAC_OS_X_VERSION_MIN_REQUIRED) && __MAC_OS_X_VERSION_MIN_REQUIRED < __MAC_10_6
#error "_DARWIN_UNLIMITED_STREAMS specified, but -mmacosx-version-min version does not support it."
#endif
#endif

/* ANSI-C */

__BEGIN_DECLS
void	 clearerr(FILE *);
int	 fclose(FILE *);
int	 feof(FILE *);
int	 ferror(FILE *);
int	 fflush(FILE *);
int	 fgetc(FILE *);
int	 fgetpos(FILE * __restrict, fpos_t *);
char	*fgets(char * __restrict, int, FILE *);
#if defined(_DARWIN_UNLIMITED_STREAMS) || defined(_DARWIN_C_SOURCE)
FILE	*fopen(const char * __restrict __filename, const char * __restrict __mode) __DARWIN_ALIAS_STARTING(__MAC_10_6, __IPHONE_3_2, __DARWIN_EXTSN(fopen));
#else /* !_DARWIN_UNLIMITED_STREAMS && !_DARWIN_C_SOURCE */
FILE	*fopen(const char * __restrict __filename, const char * __restrict __mode) __DARWIN_ALIAS_STARTING(__MAC_10_6, __IPHONE_2_0, __DARWIN_ALIAS(fopen));
#endif /* (DARWIN_UNLIMITED_STREAMS || _DARWIN_C_SOURCE) */
int	 fprintf(FILE * __restrict, const char * __restrict, ...) __printflike(2, 3);
int	 fputc(int, FILE *);
int	 fputs(const char * __restrict, FILE * __restrict) __DARWIN_ALIAS(fputs);
size_t	 fread(void * __restrict __ptr, size_t __size, size_t __nitems, FILE * __restrict __stream);
FILE	*freopen(const char * __restrict, const char * __restrict,
                 FILE * __restrict) __DARWIN_ALIAS(freopen);
int	 fscanf(FILE * __restrict, const char * __restrict, ...) __scanflike(2, 3);
int	 fseek(FILE *, long, int);
int	 fsetpos(FILE *, const fpos_t *);
long	 ftell(FILE *);
size_t	 fwrite(const void * __restrict __ptr, size_t __size, size_t __nitems, FILE * __restrict __stream) __DARWIN_ALIAS(fwrite);
int	 getc(FILE *);
int	 getchar(void);

#if !defined(_POSIX_C_SOURCE)
__deprecated_msg("This function is provided for compatibility reasons only.  Due to security concerns inherent in the design of gets(3), it is highly recommended that you use fgets(3) instead.")
#endif
char	*gets(char *);

void	 perror(const char *) __cold;
int	 printf(const char * __restrict, ...) __printflike(1, 2);
int	 putc(int, FILE *);
int	 putchar(int);
int	 puts(const char *);
int	 remove(const char *);
int	 rename (const char *__old, const char *__new);
void	 rewind(FILE *);
int	 scanf(const char * __restrict, ...) __scanflike(1, 2);
void	 setbuf(FILE * __restrict, char * __restrict);
int	 setvbuf(FILE * __restrict, char * __restrict, int, size_t);

__swift_unavailable("Use snprintf instead.")
#if !defined(_POSIX_C_SOURCE)
__deprecated_msg("This function is provided for compatibility reasons only.  Due to security concerns inherent in the design of sprintf(3), it is highly recommended that you use snprintf(3) instead.")
#endif
int	 sprintf(char * __restrict, const char * __restrict, ...) __printflike(2, 3);

int	 sscanf(const char * __restrict, const char * __restrict, ...) __scanflike(2, 3);
FILE	*tmpfile(void);

__swift_unavailable("Use mkstemp(3) instead.")
#if !defined(_POSIX_C_SOURCE)
__deprecated_msg("This function is provided for compatibility reasons only.  Due to security concerns inherent in the design of tmpnam(3), it is highly recommended that you use mkstemp(3) instead.")
#endif
char	*tmpnam(char *);

int	 ungetc(int, FILE *);
int	 vfprintf(FILE * __restrict, const char * __restrict, va_list) __printflike(2, 0);
int	 vprintf(const char * __restrict, va_list) __printflike(1, 0);

__swift_unavailable("Use vsnprintf instead.")
#if !defined(_POSIX_C_SOURCE)
__deprecated_msg("This function is provided for compatibility reasons only.  Due to security concerns inherent in the design of sprintf(3), it is highly recommended that you use vsnprintf(3) instead.")
#endif
int	 vsprintf(char * __restrict, const char * __restrict, va_list) __printflike(2, 0);
__END_DECLS



/* Additional functionality provided by:
 * POSIX.1-1988
 */

#if __DARWIN_C_LEVEL >= 198808L
#define	L_ctermid	1024	/* size for ctermid(); PATH_MAX */

__BEGIN_DECLS
#include <_ctermid.h>

#if defined(_DARWIN_UNLIMITED_STREAMS) || defined(_DARWIN_C_SOURCE)
FILE	*fdopen(int, const char *) __DARWIN_ALIAS_STARTING(__MAC_10_6, __IPHONE_3_2, __DARWIN_EXTSN(fdopen));
#else /* !_DARWIN_UNLIMITED_STREAMS && !_DARWIN_C_SOURCE */
FILE	*fdopen(int, const char *) __DARWIN_ALIAS_STARTING(__MAC_10_6, __IPHONE_2_0, __DARWIN_ALIAS(fdopen));
#endif /* (DARWIN_UNLIMITED_STREAMS || _DARWIN_C_SOURCE) */
int	 fileno(FILE *);
__END_DECLS
#endif /* __DARWIN_C_LEVEL >= 198808L */


/* Additional functionality provided by:
 * POSIX.2-1992 C Language Binding Option
 */

#if __DARWIN_C_LEVEL >= 199209L
__BEGIN_DECLS
int	 pclose(FILE *) __swift_unavailable("Use posix_spawn APIs or NSTask instead. (On iOS, process spawning is unavailable.)");
#if defined(_DARWIN_UNLIMITED_STREAMS) || defined(_DARWIN_C_SOURCE)
FILE	*popen(const char *, const char *) __DARWIN_ALIAS_STARTING(__MAC_10_6, __IPHONE_3_2, __DARWIN_EXTSN(popen)) __swift_unavailable("Use posix_spawn APIs or NSTask instead. (On iOS, process spawning is unavailable.)");
#else /* !_DARWIN_UNLIMITED_STREAMS && !_DARWIN_C_SOURCE */
FILE	*popen(const char *, const char *) __DARWIN_ALIAS_STARTING(__MAC_10_6, __IPHONE_2_0, __DARWIN_ALIAS(popen)) __swift_unavailable("Use posix_spawn APIs or NSTask instead. (On iOS, process spawning is unavailable.)");
#endif /* (DARWIN_UNLIMITED_STREAMS || _DARWIN_C_SOURCE) */
__END_DECLS
#endif /* __DARWIN_C_LEVEL >= 199209L */

/* Additional functionality provided by:
 * POSIX.1c-1995,
 * POSIX.1i-1995,
 * and the omnibus ISO/IEC 9945-1: 1996
 */

#if __DARWIN_C_LEVEL >= 199506L

/* Functions internal to the implementation. */
__BEGIN_DECLS
int	__srget(FILE *);
int	__svfscanf(FILE *, const char *, va_list) __scanflike(2, 0);
int	__swbuf(int, FILE *);
__END_DECLS

/*
 * The __sfoo macros are here so that we can
 * define function versions in the C library.
 */
#define	__sgetc(p) (--(p)->_r < 0 ? __srget(p) : (int)(*(p)->_p++))
#if defined(__GNUC__) && defined(__STDC__)
__header_always_inline int __sputc(int _c, FILE *_p) {
	if (--_p->_w >= 0 || (_p->_w >= _p->_lbfsize && (char)_c != '\n'))
		return (*_p->_p++ = _c);
	else
		return (__swbuf(_c, _p));
}
#else
/*
 * This has been tuned to generate reasonable code on the vax using pcc.
 */
#define	__sputc(c, p) \
	(--(p)->_w < 0 ? \
		(p)->_w >= (p)->_lbfsize ? \
			(*(p)->_p = (c)), *(p)->_p != '\n' ? \
				(int)*(p)->_p++ : \
				__swbuf('\n', p) : \
			__swbuf((int)(c), p) : \
		(*(p)->_p = (c), (int)*(p)->_p++))
#endif

#define	__sfeof(p)	(((p)->_flags & __SEOF) != 0)
#define	__sferror(p)	(((p)->_flags & __SERR) != 0)
#define	__sclearerr(p)	((void)((p)->_flags &= ~(__SERR|__SEOF)))
#define	__sfileno(p)	((p)->_file)

__BEGIN_DECLS
void	 flockfile(FILE *);
int	 ftrylockfile(FILE *);
void	 funlockfile(FILE *);
int	 getc_unlocked(FILE *);
int	 getchar_unlocked(void);
int	 putc_unlocked(int, FILE *);
int	 putchar_unlocked(int);

/* Removed in Issue 6 */
#if !defined(_POSIX_C_SOURCE) || _POSIX_C_SOURCE < 200112L
int	 getw(FILE *);
int	 putw(int, FILE *);
#endif

__swift_unavailable("Use mkstemp(3) instead.")
#if !defined(_POSIX_C_SOURCE)
__deprecated_msg("This function is provided for compatibility reasons only.  Due to security concerns inherent in the design of tempnam(3), it is highly recommended that you use mkstemp(3) instead.")
#endif
char	*tempnam(const char *__dir, const char *__prefix) __DARWIN_ALIAS(tempnam);
__END_DECLS

#ifndef lint
#define	getc_unlocked(fp)	__sgetc(fp)
#define putc_unlocked(x, fp)	__sputc(x, fp)
#endif /* lint */

#define	getchar_unlocked()	getc_unlocked(stdin)
#define	putchar_unlocked(x)	putc_unlocked(x, stdout)
#endif /* __DARWIN_C_LEVEL >= 199506L */



/* Additional functionality provided by:
 * POSIX.1-2001
 * ISO C99
 */

#if __DARWIN_C_LEVEL >= 200112L
#include <sys/_types/_off_t.h>

__BEGIN_DECLS
int	 fseeko(FILE * __stream, off_t __offset, int __whence);
off_t	 ftello(FILE * __stream);
__END_DECLS
#endif /* __DARWIN_C_LEVEL >= 200112L */

#if __DARWIN_C_LEVEL >= 200112L || defined(_C99_SOURCE) || defined(__cplusplus)
__BEGIN_DECLS
int	 snprintf(char * __restrict __str, size_t __size, const char * __restrict __format, ...) __printflike(3, 4);
int	 vfscanf(FILE * __restrict __stream, const char * __restrict __format, va_list) __scanflike(2, 0);
int	 vscanf(const char * __restrict __format, va_list) __scanflike(1, 0);
int	 vsnprintf(char * __restrict __str, size_t __size, const char * __restrict __format, va_list) __printflike(3, 0);
int	 vsscanf(const char * __restrict __str, const char * __restrict __format, va_list) __scanflike(2, 0);
__END_DECLS
#endif /* __DARWIN_C_LEVEL >= 200112L || defined(_C99_SOURCE) || defined(__cplusplus) */



/* Additional functionality provided by:
 * POSIX.1-2008
 */

#if __DARWIN_C_LEVEL >= 200809L
#include <sys/_types/_ssize_t.h>

__BEGIN_DECLS
int	dprintf(int, const char * __restrict, ...) __printflike(2, 3) __OSX_AVAILABLE_STARTING(__MAC_10_7, __IPHONE_4_3);
int	vdprintf(int, const char * __restrict, va_list) __printflike(2, 0) __OSX_AVAILABLE_STARTING(__MAC_10_7, __IPHONE_4_3);
ssize_t getdelim(char ** __restrict __linep, size_t * __restrict __linecapp, int __delimiter, FILE * __restrict __stream) __OSX_AVAILABLE_STARTING(__MAC_10_7, __IPHONE_4_3);
ssize_t getline(char ** __restrict __linep, size_t * __restrict __linecapp, FILE * __restrict __stream) __OSX_AVAILABLE_STARTING(__MAC_10_7, __IPHONE_4_3);
FILE *fmemopen(void * __restrict __buf, size_t __size, const char * __restrict __mode) __API_AVAILABLE(macos(10.13), ios(11.0), tvos(11.0), watchos(4.0));
FILE *open_memstream(char **__bufp, size_t *__sizep) __API_AVAILABLE(macos(10.13), ios(11.0), tvos(11.0), watchos(4.0));
__END_DECLS
#endif /* __DARWIN_C_LEVEL >= 200809L */



/* Darwin extensions */

#if __DARWIN_C_LEVEL >= __DARWIN_C_FULL
__BEGIN_DECLS
extern __const int sys_nerr;		/* perror(3) external variables */
extern __const char *__const sys_errlist[];

int	 asprintf(char ** __restrict, const char * __restrict, ...) __printflike(2, 3);
char	*ctermid_r(char *);
char	*fgetln(FILE *, size_t *);
__const char *fmtcheck(const char *, const char *) __attribute__((format_arg(2)));
int	 fpurge(FILE *);
void	 setbuffer(FILE *, char *, int);
int	 setlinebuf(FILE *);
int	 vasprintf(char ** __restrict, const char * __restrict, va_list) __printflike(2, 0);


/*
 * Stdio function-access interface.
 */
FILE	*funopen(const void *,
                 int (* _Nullable)(void *, char *, int),
                 int (* _Nullable)(void *, const char *, int),
                 fpos_t (* _Nullable)(void *, fpos_t, int),
                 int (* _Nullable)(void *));
__END_DECLS
#define	fropen(cookie, fn) funopen(cookie, fn, 0, 0, 0)
#define	fwopen(cookie, fn) funopen(cookie, 0, fn, 0, 0)

#define	feof_unlocked(p)	__sfeof(p)
#define	ferror_unlocked(p)	__sferror(p)
#define	clearerr_unlocked(p)	__sclearerr(p)
#define	fileno_unlocked(p)	__sfileno(p)

#endif /* __DARWIN_C_LEVEL >= __DARWIN_C_FULL */


#ifdef _USE_EXTENDED_LOCALES_
#include <xlocale/_stdio.h>
#endif /* _USE_EXTENDED_LOCALES_ */

#if defined (__GNUC__) && _FORTIFY_SOURCE > 0 && !defined (__cplusplus)
/* Security checking functions.  */
#include <secure/_stdio.h>
#endif

#endif /* _STDIO_H_ */

可以看到这里面还有很多的#include导入了其他的包，以及相关的逻辑（逻辑这个词是从古希腊哲学家发明而来的，最早叫做逻各斯，在编程里，逻辑代表处理输入数据的算法或业务处理）。

可以还看到一些其他的C语言系统关键字：

#define	__SNPT	0x0800		/* do not do fseek() optimisation */

上面这个define就是定义一个变量，这里明显能看出来这是定义的一个全局变量，因为它（__SNPT）在其他方法的外层。

相关

C语言是计算机最基础的语言之一，广泛应用于操作系统、嵌入式系统、数据库、游戏开发等领域。C语言的特点是高效、灵活、可移植，因此在许多需要高性能、低成本的应用场景中被广泛使用。

以下是一些使用C语言的行业：

• 操作系统：C语言是许多操作系统的核心语言，包括Windows、Linux、Mac OS X等。
• 嵌入式系统：C语言是嵌入式系统的首选语言，因为它具有高效、灵活、可移植的特点。
• 数据库：C语言是许多数据库系统的核心语言，包括MySQL、Oracle、PostgreSQL等。
• 游戏开发：C语言是许多游戏引擎的核心语言，包括Unity、Unreal Engine、CryEngine等。

C语言是一门非常强大的语言，它可以用于开发各种各样的应用程序。如果您想成为一名软件开发人员，那么学习C语言是一个很好的选择。

看到上面C语言能做的东西，比如开发一套操作系统，或者开发一种数据库，说实在的这些着实让人佩服，但是要学会开发这些肯定要掌握得非常牢靠的。就像马斯克不烧那么多钱搞火箭发射，最后星舰或者星链也不会那么成功的部署发射。

再看下C语言源码包这个注释：

Copyright (c) 2000, 2005, 2007, 2009, 2010 Apple Inc. All rights reserved.

因为我用Mac做开发，所以C语言的版本好像是隶属于Apple公司的编译版本。
好，这次大概了解这些，下一次主要讲述C语言的变量分类。

作者：ukyo--BlackJesus