1. sizeof可以用类型做参数，也可以用数组、指针，对象和函数做参数；strlen只能用char*做参数，且必须是以‘‘\0‘‘结尾，当数组名作为参数传入时，实际上数组就退化成指针了。
2. sizeof返回存储对象实际占用的字节大小；strlen的功能是返回字符串的长度，遇到/0就停止，不包含/0。
3. sizeof是运算符，其值在编译时就计算好了；strlen是函数，其值要在运行时才能计算。
下面以代码为例进行解释：
#include <iostream>
using namespace std;
void test(char p[])
{
cout << "p: " << p << " " << strlen(p) << " " << sizeof(p) << endl;
//p: hello 5 4
return;
}
int main()
{
//char p[] = "hello";
//char* p1 = p;
//cout << "p1: " << p1 << " " << strlen(p1) << " " << sizeof(p1) << endl;
////p1: hello 5 4
//test(p);//将p传入到函数中，其退化为指针，sizeof(p)==4，指针占4个字节
//cout << "p: " << p << " " << strlen(p) << " " << sizeof(p) << endl;
////p: hello 5 6
//char p1[] = "hello\0";
//cout << "p1: " << p1 << " " << strlen(p1) << " " << sizeof(p1) << endl;
////p1: hello 5 7
//char p2[] = "hello\\0";// "\\"转义为"\"，所以该部分不含\0
//cout << "p2: " << p2 << " " << strlen(p2) << " " << sizeof(p2) << endl;
////p2: hello\0 7 8
//char p3[] = "hello\\\0";
//cout << "p3: " << p3 << " " << strlen(p3) << " " << sizeof(p3) << endl;
////p3: hello\ 6 8
//char p4[] = "hel\0lo";
//cout << "p4: " << p4 << " " << strlen(p4) << " " << sizeof(p4) << endl;
////p4: hel 3 7
//char p5[] = "hel\\0lo";
//cout << "p5: " << p5 << " " << strlen(p5) << " " << sizeof(p5) << endl;
////p5: hel\0lo 7 8
//char a[] = { 1,2,3,4,5 };
////strlen求长度遇到/0停止，而这种情况/0出现的位置不确定
//cout << strlen(a) << " " << sizeof(a) << endl;//警告！！！可能没有为字符串a添加终止值
//// 值不确定 5
//int a[] = { 1,2,3,4,5 };
////strlen求长度遇到/0停止，而这种情况/0出现的位置不确定
//cout << sizeof(a) << endl;
//// 20
//const char *p = "hello";
//cout << "p: " << p << " " << strlen(p) << " " << sizeof(p) << endl;
////p: hello 5 4
int* a[10];//数组a中每个元素均为一个指针
int b[10];//数组b中的每个元素均为一个整数
int (*c)[10];//c为一个指针
cout << sizeof(a) << " " << sizeof(b) << " " << sizeof(c) << endl;
// 40 40 4
return 0;
}
原文：https://www.cnblogs.com/yongjin-hou/p/14647687.html