【发布时间】：2023-04-02 08:58:01
【问题描述】：
我正在尝试将数据写入内存映射文件并且它显示垃圾。不知道我做错了什么。我正在创建一个内存映射文件并将 int 写入它。我看到垃圾输出。
我以读/写方式打开的文件，理想情况下我希望其他进程读取写入其中的数据
代码如下
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/mman.h>
#define FILEPATH "test"
#define NUMINTS (1000)
#define FILESIZE (NUMINTS * sizeof(int))
int main(int argc, char *argv[])
{
int i;
int fd;
int result;
int *map; /* mmapped array of int's */
/* Open a file for writing.
* - Creating the file if it doesn't exist.
* - Truncating it to 0 size if it already exists. (not really needed)
*
* Note: "O_WRONLY" mode is not sufficient when mmaping.
*/
fd = open(FILEPATH, O_RDWR | O_CREAT | O_TRUNC, (mode_t)0600);
if (fd == -1) {
perror("Error opening file for writing");
exit(EXIT_FAILURE);
}
/* Stretch the file size to the size of the (mmapped) array of ints
*/
result = lseek(fd, FILESIZE-1, SEEK_SET);
if (result == -1) {
close(fd);
perror("Error calling lseek() to 'stretch' the file");
exit(EXIT_FAILURE);
}
/* Something needs to be written at the end of the file to
* have the file actually have the new size.
* Just writing an empty string at the current file position will do.
*
* Note:
* - The current position in the file is at the end of the stretched
* file due to the call to lseek().
* - An empty string is actually a single '\0' character, so a zero-byte
* will be written at the last byte of the file.
*/
result = write(fd, "", 1);
if (result != 1) {
close(fd);
perror("Error writing last byte of the file");
exit(EXIT_FAILURE);
}
/* Now the file is ready to be mmapped.
*/
map = mmap(0, FILESIZE, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
if (map == MAP_FAILED) {
close(fd);
perror("Error mmapping the file");
exit(EXIT_FAILURE);
}
/* Now write int's to the file as if it were memory (an array of ints).
*/
for (i = 1; i <=10; ++i) {
map[i] = i;
}
/* Don't forget to free the mmapped memory
*/
if (munmap(map, FILESIZE) == -1) {
perror("Error un-mmapping the file");
/* Decide here whether to close(fd) and exit() or not. Depends... */
}
/* Un-mmaping doesn't close the file, so we still need to do that.
*/
close(fd);
return 0;
}
【问题讨论】：
-
你能检查一下输出文件的十六进制转储吗？
-
您如何验证您的结果？通过在 text 编辑器中打开文件？
map[i] = i;创建 二进制 数据。如果使用文本工具查看，它将看起来像垃圾。 -
糟糕，我的错.. hexdump 显示正确的输出。如何编写文本数据而不是二进制数据？
-
那就是
printf()然后... -
@DevSolar 我认为您的意思是
snprintf，因为 OP 需要输出到缓冲区而不是stdout。
标签： c