C++-json(2)-unsigned char-unsigned char*-memcpy-strcpy-sizeof-strlen

1.类型转换：

//1.赋值一个不知道长度的字符串
 
unsigned char s[] = "kobe8llJfFwFSPiy";                 //1.用一个字符串初始化变量
unsigned int s_length = strlen((char*)s);               //2.获取字符串长度
 
 
//2.字符串里有双引号"" 需要加\   长度数据类型：size_t
const  unsigned char sjson[] = "{\"name\":\"MABMEC3F8\", \"value\" : \"W6tvvyYEF7ZkFH8V\" }"; 
size_t sjson_length = strlen((char*)sjson);
 
 
//3.两个 unsigned char*之间的拷贝：unsigned char* pSrc, unsigned char* pDest
 
unsigned char* pSrc="ABC123";
size_t npSrclen =strlen((char*)pSrc);
unsigned char* pDest=new unsigned char[npSrclen];
memcpy(pDest, pSrc, npSrclen);

//1.static_cast      相近类型
 
 
#include
using namespace std;
 
int main()
{
	double d = 12.34;
	int a = static_cast<int>(d);
	return 0;
}
 
 
//2.reinterpret_cast 不相关类型
typedef void(*FUNC) ();
 
int DoSomething(int i)
{
	cout << "DoSomething" << endl;
	return 0;
}
int main()
{
//reinterpret_cast可以让编译器以FUNC的定义方式去看待DoSomething函数
//所以非常的BUG,下面的转换函数指针的代码时不可移植的，所以不建议使用
//C++不保证所有的函数指针都被一样使用，所以这样用有时会产生不确定的结果
	FUNC f = reinterpret_cast(DoSomething);
	f();
	system("pause");
	return 0;
}
 
 
//3.const_cast  删除变量的const属性
int main()
{
	volatile const int a = 2;
	int* p = const_cast<int*>(&a);
	*p = 3;
	cout << a << endl;
	system("pause");
	return 0;
}
 
//4.explicit关键字阻止转换构造函数进行的隐式类型转换的发生
class A
{
public:
	explicit A(int a)
	{
		cout << "A(int a)" << endl;
	}
	A(const A* a)
	{
		cout << "const A* a" << endl;
	}
private:
	int _a;
};
int main()
{
	A a1(1);  //隐式转换--A tmp(1); A a2(tmp)
	A a2 = 1;
	system("pause");
	return 0;
}
 

int main()
{
    unsigned char data[] = {0x48, 0x65, 0x6C, 0x6C, 0x6F, 0x20, 0x57, 0x6F, 0x72, 0x6C, 0x64};
    int len = sizeof(data) / sizeof(unsigned char);
    string str(data, data+len);
    return 0;
}

3.  拷贝 一定要new 

//1. 不new
unsigned char* pSrc1 = (unsigned char*)(s_data_offset_.c_str());
int  Srclen1 = strlen((char*)pSrc1);
unsigned char pcopy1[] = { 0 };      
memcpy(pcopy1, pSrc1, Srclen1 );      //debug 显示字符串中的字符无效  
int  copy1len = strlen((char*)pcopy1); //长度   24个  0x18  
 
 
//2.new  长度变了  16->21个 多出的字符为空字符
unsigned char* pSrc2 = (unsigned char*)(s_data_offset_.c_str());
int Srclen2 = strlen((char*)pSrc2);
//int m_sconst = static_cast(Srclen2);  变量变常量
unsigned char* pcopy2 = new unsigned char[Srclen2];  //长度  21个  0x15
memcpy(pcopy2, pSrc2, Srclen2 );                     //pcopy2 显示 pSrc中的字符
size_t copy2len = strlen((char*)pcopy2);
 
 
//3.去掉后面的字符串
 unsigned char*  pcopy3 = mytrim(pcopy2, Srclen2);
 size_t copy3len = strlen((char*)pcopy3);

4.copy 出来的是有空字符串的
            去掉空字符串

 //3.去掉  原始的是16-实际的是21 相差5个
  //字符串去空格
unsigned char* mytrim(unsigned char* pSrc, int pSrcLen)
{
    unsigned char* copy = (unsigned char*)malloc(pSrcLen);
    memset(copy, 0, pSrcLen);
    unsigned int i = 0, j = 0;
    for (i = 0; i < pSrcLen; i++)
    {
        if (pSrc[i] != ' ')
        {
            copy[j++] = pSrc[i];
 
        }
    }
    copy[j] = '\0';
    int  strCopy2len = strlen((char*)copy);
    return copy;
}

5.数据长度

strlen() 只有遇到'\0'才会停止计算，同时计算的长度不包含'\0',否则就是个随机值。

#include 
#include 
 
//当计算长度时，只有遇到'\0'才会停止计算，同时计算的长度不包含'\0'。
int main()
{
	char arr[10] = "abcde";
	int num = strlen(arr);
	printf("数组arr的长度为：%d\n", num);        //数据长度为5
 
	return 0;
}
 
 
int main()
{
	char arr[] = { 'a','b','c','d','e' };
	int num = strlen(arr);
	printf("数组arr的长度：%d\n", num);         //数据长度为 19 此处返回的是一个随机值
 
	return 0;
}