我正在尝试包装 read
函数来自 unistd.h
,但无法让它工作。
这是我所拥有的:(在文件中:read.raku
)
use NativeCall;
# ssize_t read(int fd, void *buf, size_t count);
sub c_read(int32 $fd, Pointer $buf is rw, size_t $count --> ssize_t) is native is symbol('read') { * }
my $buf = Buf[byte].new(0 xx 5);
my $pbuf = nativecast(Pointer, $buf);
say c_read(3, $pbuf, 5);
say '---------------------';
say $buf;
我像这样从命令行(bash)测试它:$ (exec 3< <(echo hello world); raku ./read.raku)
但我得到:5
---------------------
Buf[byte]:0x<00 00 00 00 00>
所以看起来从 FD 3 读取的字节没有写入 Buf
.我也试过这个:
use NativeCall;
# ssize_t read(int fd, void *buf, size_t count);
sub c_read(int32 $fd, Pointer $buf is rw, size_t $count --> ssize_t) is native is symbol('read') { * }
sub c_malloc(size_t $size --> Pointer) is native is symbol('malloc') { * }
my $pbuf = nativecast(Pointer[byte], c_malloc(5));
say c_read(3, $pbuf, 5);
say '---------------------';
say $pbuf[^5];
但是我遇到了段错误,我猜是因为使用 $pbuf[^5]
取消引用到未经授权的内存位置.但即使只是 $pbuf.deref
不提供读取的第一个字节。所以我一定是做错了什么或者完全误解了如何使用 native 调用。
更新:
在玩了更多之后,看起来上面第二个片段的问题在于
is rw
少量。这似乎有效:use NativeCall;
use NativeHelpers::Blob;
sub c_read(int32 $fd, Pointer $buf, size_t $count --> ssize_t) is native is symbol('read') { * }
sub c_malloc(size_t $size --> Pointer) is native is symbol('malloc') { * }
my $pbuf := nativecast(Pointer[byte], c_malloc(5));
say c_read(3, $pbuf, 5);
say '---------------------';
say $pbuf[^5]; # (104 101 108 108 111)
最佳答案
好的,所以问题出在 rw
赋予 Pointer $buf
的特征.我猜这会导致 read
函数在写入时递增指针,因此在我以后使用它时会给出错误的地址。
这是两种情况的工作代码:
use NativeCall;
# ssize_t read(int fd, void *buf, size_t count);
sub c_read(int32 $fd, Pointer $buf, size_t $count --> ssize_t) is native is symbol('read') { * }
# Passing a pointer to a Buf directly:
{
my $buf = Buf[byte].new(0 xx 5);
my $pbuf = nativecast(Pointer[byte], $buf);
say c_read(3, $pbuf, 5);
say '---------------------';
say $buf;
}
# Using malloc also works:
{
sub c_malloc(size_t $size --> Pointer) is native is symbol('malloc') { * }
my $pbuf = nativecast(Pointer[byte], c_malloc(5));
say c_read(3, $pbuf, 5);
say '---------------------';
say $pbuf[^5];
}
像这样测试它:$ (exec 3< <(echo hello world); perl6 ./read.raku)
5
---------------------
Buf[byte]:0x<68 65 6C 6C 6F>
5
---------------------
(32 119 111 114 108)
关于Raku 如何将指向 Buf 的指针传递给本地调用进行写入,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/63126852/