怎样找到C语言本身的源码（比如stdio），对学习C语言有帮助吗？

一、下载地址

如果你不想知道步骤，只想下载源码，这是2021-08-01发布的glibc-3.24的下载地址：

https://ftp.gnu.org/gnu/libc/glibc-2.34.tar.gz

二、怎么知道从哪里下载

stackoverflow上有一个问题：Where can I find the source code for all the C standard libraries?，其中有一个答案提到了glibc官网。
在glibc官网页面点这里：
在详情页面搜索download
来到了gnu的ftp服务器，然后按版本号或年份去找对应的版本，比如2011年的在这里，点击就可以下载了：

三、C本身的源码对学习C语言有帮助吗

3.1 我的答案是：帮助不大

在上面的stackoverflow的答案中有这么一句话，意思是：所有人都建议你不要去看C语言的具体实现。（前人走弯路的经验啊）

我没信这个邪，偏要去下载。然后我看到：

3.2 `printf`源码

printf方法定义在glibc-2.34/stdio-common/printf.c文件中，代码如下：

int
__printf (const char *format, ...)
{va_list arg;int done;va_start (arg, format);done = __vfprintf_internal (stdout, format, arg, 0);va_end (arg);return done;
}

里面调用了__vfprintf_internal方法

3.3 `__vfprintf_internal`的源码

__vfprintf_internal方法定义在glibc-2.34/stdio-common/vfprintf-internal.c文件中，__vfprintf_internal是vfprintf方法的别名（# define vfprintf __vfprintf_internal），vfprintf方法的代码如下（我已经看不懂这段300多行的代码了）：

int
vfprintf (FILE *s, const CHAR_T *format, va_list ap, unsigned int mode_flags)
{/* The character used as thousands separator.  */THOUSANDS_SEP_T thousands_sep = 0;/* The string describing the size of groups of digits.  */const char *grouping;/* Place to accumulate the result.  */int done;/* Current character in format string.  */const UCHAR_T *f;/* End of leading constant string.  */const UCHAR_T *lead_str_end;/* Points to next format specifier.  */const UCHAR_T *end_of_spec;/* Buffer intermediate results.  */CHAR_T work_buffer[WORK_BUFFER_SIZE];CHAR_T *workend;/* We have to save the original argument pointer.  */va_list ap_save;/* Count number of specifiers we already processed.  */int nspecs_done;/* For the %m format we may need the current `errno' value.  */int save_errno = errno;/* 1 if format is in read-only memory, -1 if it is in writable memory,0 if unknown.  */int readonly_format = 0;/* Orient the stream.  */
#ifdef ORIENTORIENT;
#endif/* Sanity check of arguments.  */ARGCHECK (s, format);#ifdef ORIENT/* Check for correct orientation.  */if (_IO_vtable_offset (s) == 0&& _IO_fwide (s, sizeof (CHAR_T) == 1 ? -1 : 1)!= (sizeof (CHAR_T) == 1 ? -1 : 1))/* The stream is already oriented otherwise.  */return EOF;
#endifif (UNBUFFERED_P (s))/* Use a helper function which will allocate a local temporary bufferfor the stream and then call us again.  */return buffered_vfprintf (s, format, ap, mode_flags);/* Initialize local variables.  */done = 0;grouping = (const char *) -1;
#ifdef __va_copy/* This macro will be available soon in gcc's <stdarg.h>.  We need itsince on some systems `va_list' is not an integral type.  */__va_copy (ap_save, ap);
#elseap_save = ap;
#endifnspecs_done = 0;#ifdef COMPILE_WPRINTF/* Find the first format specifier.  */f = lead_str_end = __find_specwc ((const UCHAR_T *) format);
#else/* Find the first format specifier.  */f = lead_str_end = __find_specmb ((const UCHAR_T *) format);
#endif/* Lock stream.  */_IO_cleanup_region_start ((void (*) (void *)) &_IO_funlockfile, s);_IO_flockfile (s);/* Write the literal text before the first format.  */outstring ((const UCHAR_T *) format,lead_str_end - (const UCHAR_T *) format);/* If we only have to print a simple string, return now.  */if (*f == L_('\0'))goto all_done;/* Use the slow path in case any printf handler is registered.  */if (__glibc_unlikely (__printf_function_table != NULL|| __printf_modifier_table != NULL|| __printf_va_arg_table != NULL))goto do_positional;/* Process whole format string.  */do{STEP0_3_TABLE;STEP4_TABLE;union printf_arg *args_value;    /* This is not used here but ... */int is_negative; /* Flag for negative number.  */union{unsigned long long int longlong;unsigned long int word;} number;int base;union printf_arg the_arg;CHAR_T *string; /* Pointer to argument string.  */int alt = 0; /* Alternate format.  */int space = 0; /* Use space prefix if no sign is needed.  */int left = 0; /* Left-justify output.  */int showsign = 0;   /* Always begin with plus or minus sign.  */int group = 0; /* Print numbers according grouping rules.  */int is_long_double = 0; /* Argument is long double/ long long int.  */int is_short = 0; /* Argument is short int.  */int is_long = 0;  /* Argument is long int.  */int is_char = 0;   /* Argument is promoted (unsigned) char.  */int width = 0; /* Width of output; 0 means none specified.  */int prec = -1;  /* Precision of output; -1 means none specified.  *//* This flag is set by the 'I' modifier and selects the use of the`outdigits' as determined by the current locale.  */int use_outdigits = 0;UCHAR_T pad = L_(' ');/* Padding character.  */CHAR_T spec;workend = work_buffer + WORK_BUFFER_SIZE;/* Get current character in format string.  */JUMP (*++f, step0_jumps);/* ' ' flag.  */LABEL (flag_space):space = 1;JUMP (*++f, step0_jumps);/* '+' flag.  */LABEL (flag_plus):showsign = 1;JUMP (*++f, step0_jumps);/* The '-' flag.  */LABEL (flag_minus):left = 1;pad = L_(' ');JUMP (*++f, step0_jumps);/* The '#' flag.  */LABEL (flag_hash):alt = 1;JUMP (*++f, step0_jumps);/* The '0' flag.  */LABEL (flag_zero):if (!left)pad = L_('0');JUMP (*++f, step0_jumps);/* The '\'' flag.  */LABEL (flag_quote):group = 1;if (grouping == (const char *) -1){#ifdef COMPILE_WPRINTFthousands_sep = _NL_CURRENT_WORD (LC_NUMERIC,_NL_NUMERIC_THOUSANDS_SEP_WC);
#elsethousands_sep = _NL_CURRENT (LC_NUMERIC, THOUSANDS_SEP);
#endifgrouping = _NL_CURRENT (LC_NUMERIC, GROUPING);if (*grouping == '\0' || *grouping == CHAR_MAX
#ifdef COMPILE_WPRINTF|| thousands_sep == L'\0'
#else|| *thousands_sep == '\0'
#endif)grouping = NULL;}JUMP (*++f, step0_jumps);LABEL (flag_i18n):use_outdigits = 1;JUMP (*++f, step0_jumps);/* Get width from argument.  */LABEL (width_asterics):{const UCHAR_T *tmp;  /* Temporary value.  */tmp = ++f;if (ISDIGIT (*tmp)){int pos = read_int (&tmp);if (pos == -1){__set_errno (EOVERFLOW);done = -1;goto all_done;}if (pos && *tmp == L_('$'))/* The width comes from a positional parameter.  */goto do_positional;}width = va_arg (ap, int);/* Negative width means left justified.  */if (width < 0){width = -width;pad = L_(' ');left = 1;}}JUMP (*f, step1_jumps);/* Given width in format string.  */LABEL (width):width = read_int (&f);if (__glibc_unlikely (width == -1)){__set_errno (EOVERFLOW);done = -1;goto all_done;}if (*f == L_('$'))/* Oh, oh.  The argument comes from a positional parameter.  */goto do_positional;JUMP (*f, step1_jumps);LABEL (precision):++f;if (*f == L_('*')){const UCHAR_T *tmp;   /* Temporary value.  */tmp = ++f;if (ISDIGIT (*tmp)){int pos = read_int (&tmp);if (pos == -1){__set_errno (EOVERFLOW);done = -1;goto all_done;}if (pos && *tmp == L_('$'))/* The precision comes from a positional parameter.  */goto do_positional;}prec = va_arg (ap, int);/* If the precision is negative the precision is omitted.  */if (prec < 0)prec = -1;}else if (ISDIGIT (*f)){prec = read_int (&f);/* The precision was specified in this case as an extremelylarge positive value.  */if (prec == -1){__set_errno (EOVERFLOW);done = -1;goto all_done;}}elseprec = 0;JUMP (*f, step2_jumps);/* Process 'h' modifier.  There might another 'h' following.  */LABEL (mod_half):is_short = 1;JUMP (*++f, step3a_jumps);/* Process 'hh' modifier.  */LABEL (mod_halfhalf):is_short = 0;is_char = 1;JUMP (*++f, step4_jumps);/* Process 'l' modifier.  There might another 'l' following.  */LABEL (mod_long):is_long = 1;JUMP (*++f, step3b_jumps);/* Process 'L', 'q', or 'll' modifier.  No other modifier isallowed to follow.  */LABEL (mod_longlong):is_long_double = 1;is_long = 1;JUMP (*++f, step4_jumps);LABEL (mod_size_t):is_long_double = sizeof (size_t) > sizeof (unsigned long int);is_long = sizeof (size_t) > sizeof (unsigned int);JUMP (*++f, step4_jumps);LABEL (mod_ptrdiff_t):is_long_double = sizeof (ptrdiff_t) > sizeof (unsigned long int);is_long = sizeof (ptrdiff_t) > sizeof (unsigned int);JUMP (*++f, step4_jumps);LABEL (mod_intmax_t):is_long_double = sizeof (intmax_t) > sizeof (unsigned long int);is_long = sizeof (intmax_t) > sizeof (unsigned int);JUMP (*++f, step4_jumps);/* Process current format.  */while (1){process_arg (((struct printf_spec *) NULL));process_string_arg (((struct printf_spec *) NULL));LABEL (form_unknown):if (spec == L_('\0')){/* The format string ended before the specifier is complete.  */__set_errno (EINVAL);done = -1;goto all_done;}/* If we are in the fast loop force entering the complicatedone.  */goto do_positional;}/* The format is correctly handled.  */++nspecs_done;/* Look for next format specifier.  */
#ifdef COMPILE_WPRINTFf = __find_specwc ((end_of_spec = ++f));
#elsef = __find_specmb ((end_of_spec = ++f));
#endif/* Write the following constant string.  */outstring (end_of_spec, f - end_of_spec);}while (*f != L_('\0'));/* Unlock stream and return.  */goto all_done;/* Hand off processing for positional parameters.  */
do_positional:done = printf_positional (s, format, readonly_format, ap, &ap_save,done, nspecs_done, lead_str_end, work_buffer,save_errno, grouping, thousands_sep, mode_flags);all_done:/* Unlock the stream.  */_IO_funlockfile (s);_IO_cleanup_region_end (0);return done;
}

3.4 还有很多汇编文件

在查东西的时候还发现源码里面有大量的汇编文件，比如glibc-2.34/sysdeps/x86_64/multiarch目录下的文件：

即C文件里面又调用了汇编文件里面的方法。
我已经了解一些粗浅的C语言和汇编相关的知识了，但是看C语言源码中的C文件和汇编文件基本上还是看不懂，所以如果你不是钻研C语言源码的话，建议你直接放弃~