C + + face question 5: It is recommended not to use the size of the sizeof arithmetic group in the function

C + + face question 5: It is recommended not to use the size of the sizeof arithmetic group in the function

#include <iostream>usingNamespace::STD;voidFooConst int[]);intMain () {intarr[3] = {1,2,3};cout<<"in main array size:"<<sizeof(arr)/sizeof(int) <<endl; Foo (arr);}voidFooConst intArr[]) {cout<<"in foo array size:"<<sizeof(arr)/sizeof(int) <<endl;} Output:in MainArraySize3in FooArraySize1

Note: in C + + functions, if an array is passed in as a parameter, the array is degraded to a pointer, so the length of the array is not known.
"Imperfect C + +" can use a small technique to find a function of the length of an array, using a template to intercept the length directly, because the input is an array of references (note that the array reference as the syntax of the parameter), so it can be in the compilation period to identify the pointer.

template <typenameint N>int arr_size(T (&arr)[N]){    return N;//函数直接返回作为参数传入的数组的长度。}

C + + face question 5: It is recommended not to use the size of the sizeof arithmetic group in the function