mmap的使用

参考资料

mmap 函数：原理与使用(含代码)
mmap函数使用与实例详解
Linux系统编程：mmap使用技巧
mmap和普通文件读写的区别和比较 & mmap的注意点

认真分析mmap：是什么 为什么 怎么用
github源码

一、mmap读入文件

#include<iostream>
#include<sys/mman.h>
#include<sys/types.h>
#include<fcntl.h>
#include<unistd.h>
#include<string.h>

using namespace std;
void CreateFromFile(string& FileName)
	{//由数据文件FileName创建图

		

		//size_t i;

		//打开文件，fd为文件描述符
		int fd = open(FileName.c_str(), O_RDONLY);
		//cout << "fd   " << fd << endl;

		//文件长度
		int len = lseek(fd, 0, SEEK_END);
		//cout << "len   " << len << endl;

		//文件映射
		char* data = (char*)mmap(NULL, len, PROT_READ, MAP_PRIVATE, fd, 0);

		//关闭文件，若放在此处不行就放在文件末尾munmap函数之前
		close(fd);

		auto p_end = data;
		//unsigned int num_s[3];//用来存放数据

		vector_3 value;
		while (*p_end != '\0')
		{
			for (short int i = 0; i < 3; ++i)
			{
				value.value[i] = strtoul(p_end, &p_end, 10);//将char数组转换为unsigned int类型，保存在数组num_s中
				++p_end;
				if (i < 2)
				{
					//node_set.insert(tmp_arcs[tmp_arcs_size][i]);
					//node_set[node_set_size++] = tmp_arcs.data_line[tmp_arcs_size][i];
					//node_set.insert(value.value[i]);
					node_set.push_back(value.value[i]);
				}
			}
			//tmp_arcs_size += 1;

			tmp_arcs.push_back(value);
		}
		// 解除映射，释放空间
		munmap(data, len);

		do somthing;

二、mmap写入文件

#include<iostream>
#include<sys/mman.h>
#include<sys/types.h>
#include<fcntl.h>
#include<unistd.h>
#include<string.h>

using namespace std;
void PrintResult(string& outFileName)
/*********************写入文件+交替写入+mmap写+***********************/		
	{

		do something;
		
		string total_size_s = to_string(total_size) + "\n";
		int len = total_size_s.size() + 1;
		for (int i = 0; i < THREAD_NUM; ++i)
		{
			len += answer_len[i];
		}
		// 打开文件
		int fd = open(outFileName.c_str(), O_RDWR | O_CREAT, 0666);
		//先给文件申请一个大小，写入一个字符进行保证
		lseek(fd, len - 1, 0);
		write(fd, "h", 1);//可能就是这个文件搞的鬼
		// 使用mmap函数建立内存映射
		char* addr = (char*)mmap(NULL, len, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
		// 内存映射建立好了，此时可以关闭文件了
		close(fd);
		auto iter = addr;


		memcpy(addr, total_size_s.c_str(), total_size_s.size());
		addr += total_size_s.size();


		//交替进行输出
		uint t[THREAD_NUM];
		uint process_id = 0;
		for (uint i = 0; i < 5; ++i)
		{
			for (uint j = 0; j < THREAD_NUM; ++j)
				t[j] = 0;

			process_id = 0;
			while (size[i])
			{
				for (uint j = 0; j < THREAD_NUM; ++j)
				{
					while (t[j] < result_stat[j][i].size() && result_stat[j][i][t[j]] == process_id)
					{

						memcpy(addr, result[j][i][t[j]].c, strlen(result[j][i][t[j]].c));
						addr += strlen(result[j][i][t[j]].c);

						++t[j];
						--size[i];
					}
					++process_id;

				}
			}
		}
		memcpy(addr, "\n", 1);
		munmap(iter, len);
	}

三、int型 转 字符串

void my_itoa(char* buf, unsigned int val)
	{
		unsigned int vals[10] = {};
		int len = 0;
		do
		{
			vals[len] = val % 10;
			val /= 10;
			++len;
		} while (val > 0);

		--len;
		char* p = buf;
		do
		{
			*p = vals[len] + '0';
			++p;
			--len;

		} while (len >= 0);
		*p = ',';
		++p;
		*p = '\0';
	}

四、unsigned int型 转 字符串(通过查询的方式)

inline void ui2S(MyContainer& a, vector<m_answer>& b, vector<uint>& c, const uint& thread_index)
	{
		c.push_back(a.base[0]);
		m_answer s_temp;
		char* p1 = s_temp.c;
		char* p2 = NULL;
		for (unsigned int i = 0; i < a.rear; ++i)
		{
			p2 = vexs[a.base[i]].id_char;///
			while (*p2 != '\0')
			{
				*p1 = *p2;
				++p1;
				++p2;
			}
		}
		*p1 = '\0';
		--p1;
		*p1 = '\n';
		answer_len[thread_index] += strlen(s_temp.c);
		b.push_back(s_temp);
	}