sizeof操作符.docVIP

深入理解sizeof　　最近在论坛里总有人问关于sizeof的问题，并且本人对这个问题也一直没有得到很好的解决，索性今天对它来个较为详细的总结，同时结合strlen进行比较，如果能对大家有点点帮助，这是我最大的欣慰了。一、好首先看看sizeof和strlen在MSDN上的定义：首先看一MSDN上如何对sizeof进行定义的： sizeof Operator sizeof expression The sizeof keyword gives the amount of storage, in bytes, associated with a variable or a type (including aggregate types). This keyword returns a value of type size_t. The expression is either an identifier or a type-cast expression (a type specifier enclosed in parentheses). When applied to a structure type or variable, sizeof returns the actual size, which may include padding bytes inserted for alignment. When applied to a statically dimensioned array, sizeof returns the size of the entire array. The sizeof operator cannot return the size of dynamically allocated arrays or external arrays. 然后再看一下对strlen是如何定义的： strlen Get the length of a string. Routine Required Header： strlen string.h size_t strlen( const char *string ); Parameter string：Null-terminated string Libraries All versions of the C run-time libraries. Return Value Each of these functions returns the number of characters in string, excluding the terminal NULL. No return value is reserved to indicate an error. Remarks Each of these functions returns the number of characters in string, not including the terminating null character. wcslen is a wide-character version of strlen; the argument of wcslen is a wide-character string. wcslen and strlen behave identically otherwise. 二、由几个例子说开去。第一个例子： char* ss = 0123456789; sizeof(ss) 结果 4 ＝＝＝》ss是指向字符串常量的字符指针 sizeof(*ss) 结果 1 ＝＝＝》*ss是第一个字符 char ss[] = 0123456789; sizeof(ss) 结果 11 ＝＝＝》ss是数组，计算到\0位置，因此是10＋1 sizeof(*ss) 结果 1 ＝＝＝》*ss是第一个字符 char ss[100] = 0123456789; sizeof(ss) 结果是100 ＝＝＝》ss表示在内存中的大小 100×1 strlen(ss) 结果是10 ＝＝＝》strlen是个函数内部实现是用一个循环计算到\0为止之前 int ss[100] = 0123456789; sizeof(ss) 结果 400 ＝＝＝》ss表示再内存中的大小 100×4 strlen(ss) 错误 ＝＝＝》strlen的参数只能是char* 且必须是以\0结尾的char q[]=abc; char p[]=a\n; sizeof(q),sizeof(p),strlen(q),strlen(p); 结果是 4 3 3 2 第二个例子： cla