vsnprintf字符串格式化输出实例：日志中打印程序名和行号

静态全局变量 c_FileName 和 i_FileLineNum 分别用于存储源程序文件名和打印函数所在的行号；
自定义标识符 PRINT 先调用源程序文件名和行号的赋值函数 Get_File_Line ，然后调用个数未知的参数的处理函数 F_vsnprintf；
类似于sprintf和snprintf这两个函数，相比vsprintf函数，vsnprintf加了最大字节( MAXBYTES )的限制，防止内存溢出。

/**
 * @FileName    vsnprintf_name_line.c
 * @Describe    A simple example for using vsnprintf to print the name and line-num of source file in linux.
 * @Author      vfhky 2016-03-13 23:28 https://typecodes.com/cseries/vsnprintffilenameline.html
 * @Compile     gcc vsnprintf_name_line.c -o vsnprintf_name_line
 */
#include <stdio.h>
#include <string.h>
#include <stdarg.h>

#define FILENAME_LEN 100
#define MAXLINE 1024
#define MAXBYTES 50

static char c_FileName[FILENAME_LEN];
static int  i_FileLineNum;

//Self-define a function which can print the name and line-number of the source file calling it.
#define PRINT Get_File_Line( __FILE__, __LINE__ );\
			  F_vsnprintf

/**
 * Get the linenum and filename of the source file.
 * @Para-in:		p_FileName:	The name of the source file.
 * @Para-in:		i_FileLine:	The line-number of the source file.
 */
void Get_File_Line( char *p_FileName, int i_FileLine )
{
    strcpy( c_FileName, p_FileName );
    i_FileLineNum = i_FileLine;
    return;
}

/**
 * Print the arguments according to the first argument, name as fmt.
 */
void F_vsnprintf( char *fmt, ... )
{
	char buf[MAXLINE] = {0x00};
	snprintf( buf, MAXBYTES, "[%s:%d] ", c_FileName, i_FileLineNum );
	va_list ap;
	va_start( ap, fmt );
	vsnprintf( buf+strlen(buf), MAXLINE, fmt, ap );
	va_end( ap );
	
	strcat( buf, "\n" );
	fflush( stdout );
	
	fputs( buf, stderr );
	fflush( NULL );
	return;
}

int main( int argc, char **argv )
{
	PRINT( "[%s]", "Hello." );
	PRINT( "[%s %s]", "Hello", "world." );
	return 0;
}