转自http://bbs.pediy.com/showthread.php?t=130889&page=2
1.宏中#的作用: 宏展开时, 如果没有遇到 # , 则会继续展开;
代码如下:
#include <stdio.h> int main () { #define Japan_EarthQuake 9.0 #define _ToStr(x) #x #define __ToStr(x) _ToStr(x) //输出Japan_EarthQuake is Japan_EarthQuake printf("Japan_EarthQuake is %s /n", _ToStr(Japan_EarthQuake)); //输出Japan_EarthQuake is 9.0 printf("Japan_EarthQuake is %s /n", __ToStr(Japan_EarthQuake)); system("pause"); return 0; }
2.描述strncpy的行为：
strncpy 的定义是：char* strncpy(char* dest, const char * source, size_t count);第一点：如果source串的长度比count长，只复制count长的串，后面不会补串结尾符'/０';第二点：如果count比source串要长，则长出的部分会全部补０;第三点：函数不检查dest的长度。如果dest分配的内存比count短，会溢出;
#include <stdio.h> int main () { char a[8]="aaaaa"; char bb[12]="bbbbbbb"; char ccc[16]="ccccccccccc"; printf("a is %s /nbb is %s /nccc is %s /n",a,bb,ccc); strncpy(ccc,a,4); printf("ccc is %s /n", ccc); strncpy(a,ccc,10); printf("a is %s /n", a);//输出aaaacccccc+乱码 strncpy(ccc,bb,10); printf("ccc is %s /n", ccc); system("pause"); return 0; }
