我有一个内存映射文件
和相应的MapViewOfFile
句柄。 内存映射文件
将包含两部分数据:
unsigned int
指定实际数据的长度- 实际相关数据
例如如果我的实际数据的长度是 10
个字符,内存映射文件将是这样的:
10
abcdefghij
其中 abcdefghij
是我想要的数据,并且会有一个换行符 b/w 长度数字和数据。如果需要,我也可以自由使用任何其他分隔符。
现在我想先读取unsigned int
,以便能够读取实际数据。我正在考虑 memcpy
但我不确定如何才能获得准确的 unsigned int 值,因为我认为 memcpy
逐字符复制。如何从内容中提取 10
?
最佳答案
你可以这样做:
#include "windows.h"
#include <iostream>
int main() {
const size_t buffer_size = 4098;
const char* name = "my_shared_memory"; //sm name
HANDLE file = CreateFileMapping(INVALID_HANDLE_VALUE, NULL, PAGE_READWRITE, 0, buffer_size, name);
LPVOID region = MapViewOfFile(file, FILE_MAP_ALL_ACCESS, 0, 0, buffer_size);
const char* const msg = "this is my data"; //this is the string you want to pass
const int msg_size = strlen(msg) + 1; //this is the size of the string data with \0
const int total_size = msg_size + sizeof(int); //the total size of your data: the size of the string and the string by itself
char* const data = (char*)malloc(total_size); //get some memory to place this data
((int*)data)[0] = msg_size; //set the first part of the data with the string msg size
memcpy(data + sizeof(int), msg, msg_size); //set the msg by it self just after the size
CopyMemory(region, data, total_size); //put on sm
const int retrieved_size = ((int*)region)[0]; //retrieves the size of the msg from the sm
char* const retrieved_msg = (char*)malloc(retrieved_size); //alloc some space for receive the msg with the retrieved size
memcpy(retrieved_msg, (char*)region + sizeof(int), retrieved_size); //set the msg in the previous allocated memory
std::cout << retrieved_msg << std::endl; //prints the msg
free(data);
free(retrieved_msg);
}
在此question您有一些解决方案来检查字节序。然后,如果需要,您可以再使用一个字节来存储此信息。如果字节顺序不同,您可以 swap bytes .
Josh 评论的解决方案:
对于 ASCII 编码的大小,您可以将其作为字符串保存,而不是将 int 二进制编码的大小存入内存:
const int max_digits_size = 3;
char number[max_digits_size + 1];
sprintf(number, "%d", msg_size);
//your total_size is now (max_digits_size + 1) + msg_size
//first you retrieve from sm the number as string in number_memcopied var, then you convert:
const int retrieved_size = strtol(number_memcopied, NULL, 10);
关于c++ - 以下场景如何复制?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/58011965/