C语言 在 C 中使用 mmap 写入内存。
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use mmap in C to write into memory.
提问by parisa
I want to use mmap()to create a file containing some integers. I want to write to this file by writing to memory. I know that the data in memory is binary format and hence the data in file will also be in binary.
Can I use mmapfor this purpose? where can I find good resources on how to use mmap? I didn't find a good manual to start with.
我想用来mmap()创建一个包含一些整数的文件。我想通过写入内存来写入这个文件。我知道内存中的数据是二进制格式，因此文件中的数据也将是二进制格式。我可以mmap用于此目的吗？我在哪里可以找到关于如何使用的好资源mmap？我没有找到一个好的手册开始。
回答by ryyker
Here is an example:
下面是一个例子：
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/mman.h> /* mmap() is defined in this header */
#include <fcntl.h>
void err_quit(char *msg)
{
printf(msg);
return 0;
}
int main (int argc, char *argv[])
{
int fdin, fdout;
char *src, *dst;
struct stat statbuf;
int mode = 0x0777;
if (argc != 3)
err_quit ("usage: a.out <fromfile> <tofile>");
/* open the input file */
if ((fdin = open (argv[1], O_RDONLY)) < 0)
{printf("can't open %s for reading", argv[1]);
return 0;
}
/* open/create the output file */
if ((fdout = open (argv[2], O_RDWR | O_CREAT | O_TRUNC, mode )) < 0)//edited here
{printf ("can't create %s for writing", argv[2]);
return 0;
}
/* find size of input file */
if (fstat (fdin,&statbuf) < 0)
{printf ("fstat error");
return 0;
}
/* go to the location corresponding to the last byte */
if (lseek (fdout, statbuf.st_size - 1, SEEK_SET) == -1)
{printf ("lseek error");
return 0;
}
/* write a dummy byte at the last location */
if (write (fdout, "", 1) != 1)
{printf ("write error");
return 0;
}
/* mmap the input file */
if ((src = mmap (0, statbuf.st_size, PROT_READ, MAP_SHARED, fdin, 0))
== (caddr_t) -1)
{printf ("mmap error for input");
return 0;
}
/* mmap the output file */
if ((dst = mmap (0, statbuf.st_size, PROT_READ | PROT_WRITE,
MAP_SHARED, fdout, 0)) == (caddr_t) -1)
{printf ("mmap error for output");
return 0;
}
/* this copies the input file to the output file */
memcpy (dst, src, statbuf.st_size);
return 0;
} /* main */
From Here
Another Linux example
Windows implementationof memory mapping.
回答by Mekap
Ressources -> mmap man 2
资源 -> mmap man 2
Examples : Linux's cpby fahmy
示例： Linux 的 cpby fahmy
if ((dst = mmap (0, statbuf.st_size, PROT_READ | PROT_WRITE,
MAP_SHARED, fdout, 0)) == (caddr_t) -1)
err_sys ("mmap error for output");
/* this copies the input file to the output file */
memcpy (dst, src, statbuf.st_size);
以及 mmap wiki 示例
#include <sys/types.h>
#include <sys/mman.h>
#include <err.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
/* Does not work on OS X, as you can't mmap over /dev/zero */
int main(void)
{
const char str1[] = "string 1";
const char str2[] = "string 2";
int parpid = getpid(), childpid;
int fd = -1;
char *anon, *zero;
if ((fd = open("/dev/zero", O_RDWR, 0)) == -1)
err(1, "open");
anon = (char*)mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_ANON|MAP_SHARED, -1, 0);
zero = (char*)mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_FILE|MAP_SHARED, fd, 0);
if (anon == MAP_FAILED || zero == MAP_FAILED)
errx(1, "either mmap");
strcpy(anon, str1);
strcpy(zero, str1);
printf("PID %d:\tanonymous %s, zero-backed %s\n", parpid, anon, zero);
switch ((childpid = fork())) {
case -1:
err(1, "fork");
/* NOTREACHED */
case 0:
childpid = getpid();
printf("PID %d:\tanonymous %s, zero-backed %s\n", childpid, anon, zero);
sleep(3);
printf("PID %d:\tanonymous %s, zero-backed %s\n", childpid, anon, zero);
munmap(anon, 4096);
munmap(zero, 4096);
close(fd);
return (EXIT_SUCCESS);
}
sleep(2);
strcpy(anon, str2);
strcpy(zero, str2);
printf("PID %d:\tanonymous %s, zero-backed %s\n", parpid, anon, zero);
munmap(anon, 4096);
munmap(zero, 4096);
close(fd);
return (EXIT_SUCCESS);
}
Try using both and adapt them for your goal.
尝试使用两者并根据您的目标调整它们。
