[英]Troubles with using memcpy with mmap
Trying to copy a file using these functions, everything goes fine until program hits the memcpy function which gives a bus error and terminates the process. 尝试使用这些函数复制文件,一切顺利,直到程序到达memcpy函数,这会产生总线错误并终止进程。
void copy_mmap(char* in, char* out){
int input_fd, output_fd;
input_fd = open (in, O_RDONLY);
if (input_fd == -1) {
printf("Error opening input file.\n");
exit(2);
}
output_fd = open(out, O_RDWR | O_CREAT, S_IWUSR | S_IRUSR);
if(output_fd == -1){
printf("Error opening output file.\n");
exit(3);
}
struct stat st;
fstat(input_fd, &st);
char* target;
target=mmap(0, st.st_size+1, PROT_READ, MAP_SHARED, input_fd, 0);
if (target==(void*) -1){
printf("Error mapping target with errno: %d.\n", errno);
exit(6);
}
char* destination;
destination=mmap(0, st.st_size+1, PROT_READ | PROT_WRITE, MAP_SHARED, output_fd, 0);
if (destination==(void*) -1){
printf("Error mapping destination with errno: %d.\n", errno);
exit(5);
}
memcpy(destination, target, st.st_size);
munmap(destination, st.st_size);
}
Failed to figure out what is wrong, as "Bus Error" isn't a descriptive error message and there isn't any much material on the internet regarding this problem. 无法弄清楚出现了什么问题,因为“总线错误”不是描述性错误消息,互联网上没有关于此问题的任何材料。
When you create the destination file as a new file, its size is 0 bytes. 将目标文件创建为新文件时,其大小为0字节。
memcpy
crashes because it tries to write data beyond the end of the file. memcpy
崩溃,因为它试图写入超出文件末尾的数据。
You can make this work by pre-sizing the destination file to the size of the source file (using ftruncate()
) before you mmap()
it. 您可以通过在
mmap()
之前将目标文件预先调整为源文件的大小(使用ftruncate()
)来完成此工作。
Also, you should pass st.st_size
as the second argument to mmap
, not st.st_size+1
. 此外,您应该将
st.st_size
作为第二个参数传递给mmap
,而不是st.st_size+1
。 st.st_size+1
tries to map a range that is larger than the size of the file, which is invalid. st.st_size+1
尝试映射大于文件大小的范围,该范围无效。
Perhaps try to use memmove? 也许尝试使用memmove? Are you not reading and writing from the same memory/file/device location?
你不是在同一个内存/文件/设备位置读写吗? Memcpy fails in such situations.
Memcpy在这种情况下失败了。
你也可以lseek到off_t fileposition = lseek(output_fd,st.st_size-1,SEEK_SET)并将一个空字符写入output_fd。
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.