在一个返回值为int型的函数中，在printf话语之后接return；返回的结果是printf输出的长度，有什么原理吗
在一个返回值为int型的函数中，在printf语句之后接return；返回的结果是printf输出的长度，有什么原理吗？
无意间发现的情况，我写了一个函数：
int test()
{
printf("test\n");
return;
}
在主函数中庸变量a=test();
输出发现a的值为5，也即test函数中printf的输出长度。
改变printf语句的输出，返回值也跟着变。
不太理解这种情况的原因是什么，有哪位可以帮忙解释一下？不胜感激！
------解决思路----------------------
printf返回平日你头发输出的长度，保存到eax中，返回函数后，认为函数的返回值在eax中。如此而已。（Win32）
理解和讨论之前请先学会如何观察！
计算机组成原理→DOS命令→汇编语言→C语言（不包括C++）、代码书写规范→数据结构、编译原理、操作系统→计算机网络、数据库原理、正则表达式→其它语言（包括C++）、架构……
对学习编程者的忠告：
多用小脑和手，少用大脑、眼睛和嘴，会更快地学会编程！
眼过千遍不如手过一遍！
书看千行不如手敲一行！
手敲千行不如单步一行！
单步源代码千行不如单步Debug版对应汇编一行！
单步Debug版对应汇编千行不如单步Release版对应汇编一行！
VC调试时按Alt+8、Alt+7、Alt+6和Alt+5,打开汇编窗口、堆栈窗口、内存窗口和寄存器窗口看每句C对应的汇编、单步执行并观察相应堆栈、内存和寄存器变化，这样过一遍不就啥都明白了吗。
对VC来说，所谓‘调试时’就是编译连接通过以后，按F10或F11键单步执行一步以后的时候，或者在某行按F9设了断点后按F5执行停在该断点处的时候。
（Turbo C或Borland C用Turbo Debugger调试,Linux或Unix下用GDB调试时,看每句C对应的汇编并单步执行观察相应内存和寄存器变化。）
printf, wprintf
Print formatted output to the standard output stream.
int printf( const char *format [, argument]... );
int wprintf( const wchar_t *format [, argument]... );
Routine Required Header Compatibility
printf <stdio.h> ANSI, Win 95, Win NT
wprintf <stdio.h> or <wchar.h> ANSI, Win 95, Win NT
For additional compatibility information, see Compatibility in the Introduction.
Libraries
LIBC.LIB Single thread static library, retail version
LIBCMT.LIB Multithread static library, retail version
MSVCRT.LIB Import library for MSVCRT.DLL, retail version
Return Value
Each of these functions returns the number of characters printed, or a negative value if an error occurs.
Parameters
format
Format control
argument
Optional arguments
Remarks
The printf function formats and prints a series of characters and values to the standard output stream, stdout. If arguments follow the format string, the format string must contain specifications that determine the output format for the arguments. printf and fprintf behave identically except that printf writes output to stdout rather than to a destination of type FILE.
wprintf is a wide-character version of printf; format is a wide-character string. wprintf and printf behave identically otherwise.
Generic-Text Routine Mappings
TCHAR.H Routine _UNICODE & _MBCS Not Defined _MBCS Defined _UNICODE Defined
_tprintf printf printf wprintf
The format argument consists of ordinary characters, escape sequences, and (if arguments follow format) format specifications. The ordinary characters and escape sequences are copied to stdout in order of their appearance. For example, the line
printf("Line one\n\t\tLine two\n");
produces the output
Line one
Line two
Format specifications always begin with a percent sign (%) and are read left to right. When printf encounters the first format specification (if any), it converts the value of the first argument after format and outputs it accordingly. The second format specification causes the second argument to be converted and output, and so on. If there are more arguments than there are format specifications, the extra arguments are ignored. The results are undefined if there are not enough arguments for all the format specifications.
Example
/* PRINTF.C: This program uses the printf and wprintf functions
* to produce formatted output.
*/
#include <stdio.h>
void main( void )
{
char ch = 'h', *string = "computer";
int count = -9234;
double fp = 251.7366;
wchar_t wch = L'w', *wstring = L"Unicode";
/* Display integers. */
printf( "Integer formats:\n"
"\tDecimal: %d Justified: %.6d Unsigned: %u\n",
count, count, count, count );
printf( "Decimal %d as:\n\tHex: %Xh C hex: 0x%x Octal: %o\n",
count, count, count, count );
/* Display in different radixes. */
printf( "Digits 10 equal:\n\tHex: %i Octal: %i Decimal: %i\n",
0x10, 010, 10 );
/* Display characters. */
printf("Characters in field (1):\n%10c%5hc%5C%5lc\n", ch, ch, wch, wch);
wprintf(L"Characters in field (2):\n%10C%5hc%5c%5lc\n", ch, ch, wch, wch);
/* Display strings. */
printf("Strings in field (1):\n%25s\n%25.4hs\n\t%S%25.3ls\n",
string, string, wstring, wstring);
wprintf(L"Strings in field (2):\n%25S\n%25.4hs\n\t%s%25.3ls\n",
string, string, wstring, wstring);
/* Display real numbers. */
printf( "Real numbers:\n\t%f %.2f %e %E\n", fp, fp, fp, fp );
/* Display pointer. */
printf( "\nAddress as:\t%p\n", &count);
/* Count characters printed. */
printf( "\nDisplay to here:\n" );
printf( "1234567890123456%n78901234567890\n", &count );
printf( "\tNumber displayed: %d\n\n", count );
}
Output
Integer formats:
Decimal: -9234 Justified: -009234 Unsigned: 4294958062
Decimal -9234 as:
Hex: FFFFDBEEh C hex: 0xffffdbee Octal: 37777755756
Digits 10 equal:
Hex: 16 Octal: 8 Decimal: 10
Characters in field (1):
h h w w
Characters in field (2):
h h w w
Strings in field (1):
computer
comp
Unicode Uni
Strings in field (2):
computer
comp
Unicode Uni
Real numbers:
251.736600 251.74 2.517366e+002 2.517366E+002
Address as: 0012FFAC
Display to here:
123456789012345678901234567890
Number displayed: 16
Floating-Point Support Routines
------解决思路----------------------
Stream I/O Routines
------解决思路----------------------
Locale Routines
See Also fopen, fprintf, scanf, sprintf, vprintf Functions
无意间发现的情况，我写了一个函数：
int test()
{
printf("test\n");
return;
}
在主函数中庸变量a=test();
输出发现a的值为5，也即test函数中printf的输出长度。
改变printf语句的输出，返回值也跟着变。
不太理解这种情况的原因是什么，有哪位可以帮忙解释一下？不胜感激！
------解决思路----------------------
printf返回平日你头发输出的长度，保存到eax中，返回函数后，认为函数的返回值在eax中。如此而已。（Win32）
计算机组成原理→DOS命令→汇编语言→C语言（不包括C++）、代码书写规范→数据结构、编译原理、操作系统→计算机网络、数据库原理、正则表达式→其它语言（包括C++）、架构……
对学习编程者的忠告：
眼过千遍不如手过一遍！
书看千行不如手敲一行！
手敲千行不如单步一行！
单步源代码千行不如单步Debug版对应汇编一行！
单步Debug版对应汇编千行不如单步Release版对应汇编一行！
VC调试时按Alt+8、Alt+7、Alt+6和Alt+5,打开汇编窗口、堆栈窗口、内存窗口和寄存器窗口看每句C对应的汇编、单步执行并观察相应堆栈、内存和寄存器变化，这样过一遍不就啥都明白了吗。
对VC来说，所谓‘调试时’就是编译连接通过以后，按F10或F11键单步执行一步以后的时候，或者在某行按F9设了断点后按F5执行停在该断点处的时候。
（Turbo C或Borland C用Turbo Debugger调试,Linux或Unix下用GDB调试时,看每句C对应的汇编并单步执行观察相应内存和寄存器变化。）
printf, wprintf
Print formatted output to the standard output stream.
int printf( const char *format [, argument]... );
int wprintf( const wchar_t *format [, argument]... );
Routine Required Header Compatibility
printf <stdio.h> ANSI, Win 95, Win NT
wprintf <stdio.h> or <wchar.h> ANSI, Win 95, Win NT
For additional compatibility information, see Compatibility in the Introduction.
Libraries
LIBC.LIB Single thread static library, retail version
LIBCMT.LIB Multithread static library, retail version
MSVCRT.LIB Import library for MSVCRT.DLL, retail version
Return Value
Each of these functions returns the number of characters printed, or a negative value if an error occurs.
Parameters
format
Format control
argument
Optional arguments
Remarks
The printf function formats and prints a series of characters and values to the standard output stream, stdout. If arguments follow the format string, the format string must contain specifications that determine the output format for the arguments. printf and fprintf behave identically except that printf writes output to stdout rather than to a destination of type FILE.
wprintf is a wide-character version of printf; format is a wide-character string. wprintf and printf behave identically otherwise.
Generic-Text Routine Mappings
TCHAR.H Routine _UNICODE & _MBCS Not Defined _MBCS Defined _UNICODE Defined
_tprintf printf printf wprintf
The format argument consists of ordinary characters, escape sequences, and (if arguments follow format) format specifications. The ordinary characters and escape sequences are copied to stdout in order of their appearance. For example, the line
printf("Line one\n\t\tLine two\n");
produces the output
Line one
Line two
Format specifications always begin with a percent sign (%) and are read left to right. When printf encounters the first format specification (if any), it converts the value of the first argument after format and outputs it accordingly. The second format specification causes the second argument to be converted and output, and so on. If there are more arguments than there are format specifications, the extra arguments are ignored. The results are undefined if there are not enough arguments for all the format specifications.
Example
/* PRINTF.C: This program uses the printf and wprintf functions
* to produce formatted output.
*/
#include <stdio.h>
void main( void )
{
char ch = 'h', *string = "computer";
int count = -9234;
double fp = 251.7366;
wchar_t wch = L'w', *wstring = L"Unicode";
/* Display integers. */
printf( "Integer formats:\n"
"\tDecimal: %d Justified: %.6d Unsigned: %u\n",
count, count, count, count );
printf( "Decimal %d as:\n\tHex: %Xh C hex: 0x%x Octal: %o\n",
count, count, count, count );
/* Display in different radixes. */
printf( "Digits 10 equal:\n\tHex: %i Octal: %i Decimal: %i\n",
0x10, 010, 10 );
/* Display characters. */
printf("Characters in field (1):\n%10c%5hc%5C%5lc\n", ch, ch, wch, wch);
wprintf(L"Characters in field (2):\n%10C%5hc%5c%5lc\n", ch, ch, wch, wch);
/* Display strings. */
printf("Strings in field (1):\n%25s\n%25.4hs\n\t%S%25.3ls\n",
string, string, wstring, wstring);
wprintf(L"Strings in field (2):\n%25S\n%25.4hs\n\t%s%25.3ls\n",
string, string, wstring, wstring);
/* Display real numbers. */
printf( "Real numbers:\n\t%f %.2f %e %E\n", fp, fp, fp, fp );
/* Display pointer. */
printf( "\nAddress as:\t%p\n", &count);
/* Count characters printed. */
printf( "\nDisplay to here:\n" );
printf( "1234567890123456%n78901234567890\n", &count );
printf( "\tNumber displayed: %d\n\n", count );
}
Output
Integer formats:
Decimal: -9234 Justified: -009234 Unsigned: 4294958062
Decimal -9234 as:
Hex: FFFFDBEEh C hex: 0xffffdbee Octal: 37777755756
Digits 10 equal:
Hex: 16 Octal: 8 Decimal: 10
Characters in field (1):
h h w w
Characters in field (2):
h h w w
Strings in field (1):
computer
comp
Unicode Uni
Strings in field (2):
computer
comp
Unicode Uni
Real numbers:
251.736600 251.74 2.517366e+002 2.517366E+002
Address as: 0012FFAC
Display to here:
123456789012345678901234567890
Number displayed: 16
Floating-Point Support Routines
------解决思路----------------------
Stream I/O Routines
------解决思路----------------------
Locale Routines
See Also fopen, fprintf, scanf, sprintf, vprintf Functions