ANSI C中没有scanf_s(),只有scanf()，scanf()在读取时不检查边界，所以可能会造成内存泄露。所以vc++2005/2008中提供了scanf_s(),在调用时，必须提供一个数字以表明最多读取多少位字符。

MSDN中例子：

// crt_scanf_s.c

// This program uses the scanf_s and wscanf_s functions

// to read formatted input.

#include <stdio.h>

int main( void )

{

int i, result;

float fp; char c, s[81];

wchar_t wc, ws[81];

result = scanf_s( "%d %f %c %C %s %S", &i, &fp, &c, 1, &wc, 1, s, 80, ws, 80 );

printf( "The number of fields input is %d\", result );

printf( "The contents are: %d %f %c %C %s %S\", i, fp, c, wc, s, ws);

result = wscanf_s( L"%d %f %hc %lc %S %ls", &i, &fp, &c, 2, &wc, 1, s, 80, ws, 80 );

wprintf( L"The number of fields input is %d\", result );

wprintf( L"The contents are: %d %f %C %c %hs %s\", i, fp, c, wc, s, ws);

return 0;

}