Assembly FCB和Int 21h/功能23h
我需要使用Int 21h/function 23h获得文件大小。我不知道FCB是如何工作的,也不知道如何使用它。本节中给出的功能23h说明如下: 函数23h(35)使用FCBs获取文件大小Assembly FCB和Int 21h/功能23h,assembly,dos,x86-16,tasm,16-bit,Assembly,Dos,X86 16,Tasm,16 Bit,我需要使用Int 21h/function 23h获得文件大小。我不知道FCB是如何工作的,也不知道如何使用它。本节中给出的功能23h说明如下: 函数23h(35)使用FCBs获取文件大小 Returns the number of records in a file. On entry: AH 23h DS:DX Pointer to an unopened FCB Returns: AL
Returns the number of records in a file.
On entry: AH 23h
DS:DX Pointer to an unopened FCB
Returns: AL 00h If matching file found
FFh If no matching file found
我该如何使用它?您链接到的同一页的底部有一个链接。如果您遵循它,您将看到您需要为FCB初始化一个内存块,并用驱动器号(03代表C:)、8.3格式的文件名和几个其他字段填充它。将ds:dx点指向该内存块,将ah设置为23h,并
int21
。如果al为0,则成功,您可以从ds:dx+10h获得文件长度
请参见偏移量0x10处与指定文件大小匹配的b2 6a 00
:
jcomeau@aspire:/tmp$ ls -l /usr/src/dosdebug/DEBUG.TXT
-rw-r--r-- 1 jcomeau jcomeau 27314 Feb 15 2014 /usr/src/dosdebug/DEBUG.TXT
jcomeau@aspire:/tmp$ printf '%x\n' 27314
6ab2
我必须修补dosbox中的一个bug才能让它工作,因此更新速度很慢
diff -up ./include/dos_inc.h.orig ./include/dos_inc.h
--- ./include/dos_inc.h.orig 2015-12-27 12:43:12.000000000 -0800
+++ ./include/dos_inc.h 2015-12-27 11:53:19.000000000 -0800
@@ -170,7 +170,7 @@ void DOS_BuildUMBChain(bool umb_active,b
bool DOS_LinkUMBsToMemChain(Bit16u linkstate);
/* FCB stuff */
-bool DOS_FCBOpen(Bit16u seg,Bit16u offset);
+Bit16u DOS_FCBOpen(Bit16u seg,Bit16u offset);
bool DOS_FCBCreate(Bit16u seg,Bit16u offset);
bool DOS_FCBClose(Bit16u seg,Bit16u offset);
bool DOS_FCBFindFirst(Bit16u seg,Bit16u offset);
diff -up ./src/dos/dos_classes.cpp.orig ./src/dos/dos_classes.cpp
diff -up ./src/dos/dos_files.cpp.orig ./src/dos/dos_files.cpp
--- ./src/dos/dos_files.cpp.orig 2015-12-27 10:08:26.000000000 -0800
+++ ./src/dos/dos_files.cpp 2015-12-27 12:22:17.000000000 -0800
@@ -964,7 +964,7 @@ bool DOS_FCBCreate(Bit16u seg,Bit16u off
return true;
}
-bool DOS_FCBOpen(Bit16u seg,Bit16u offset) {
+Bit16u DOS_FCBOpen(Bit16u seg,Bit16u offset) {
DOS_FCB fcb(seg,offset);
char shortname[DOS_FCBNAME];Bit16u handle;
fcb.GetName(shortname);
@@ -972,7 +972,7 @@ bool DOS_FCBOpen(Bit16u seg,Bit16u offse
/* First check if the name is correct */
Bit8u drive;
char fullname[DOS_PATHLENGTH];
- if (!DOS_MakeName(shortname,fullname,&drive)) return false;
+ if (!DOS_MakeName(shortname,fullname,&drive)) return (Bit16u)false;
/* Check, if file is already opened */
for (Bit8u i=0;i<DOS_FILES;i++) {
@@ -982,16 +982,16 @@ bool DOS_FCBOpen(Bit16u seg,Bit16u offse
if (handle==0xFF) {
// This shouldnt happen
LOG(LOG_FILES,LOG_ERROR)("DOS: File %s is opened but has no psp entry.",shortname);
- return false;
+ return (Bit16u)false;
}
fcb.FileOpen((Bit8u)handle);
- return true;
+ return handle;
}
}
if (!DOS_OpenFile(shortname,OPEN_READWRITE,&handle)) return false;
fcb.FileOpen((Bit8u)handle);
- return true;
+ return handle;
}
bool DOS_FCBClose(Bit16u seg,Bit16u offset) {
@@ -1181,11 +1181,12 @@ bool DOS_FCBGetFileSize(Bit16u seg,Bit16
char shortname[DOS_PATHLENGTH];Bit16u entry;Bit8u handle;Bit16u rec_size;
DOS_FCB fcb(seg,offset);
fcb.GetName(shortname);
- if (!DOS_OpenFile(shortname,OPEN_READ,&entry)) return false;
+ if (!(entry = DOS_FCBOpen(seg, offset))) return false;
handle = RealHandle(entry);
Bit32u size = 0;
Files[handle]->Seek(&size,DOS_SEEK_END);
- DOS_CloseFile(entry);fcb.GetSeqData(handle,rec_size);
+ fcb.GetSeqData(handle,rec_size);
+ DOS_CloseFile(entry);
Bit32u random=(size/rec_size);
if (size % rec_size) random++;
fcb.SetRandom(random);
diff-up./include/dos_inc.h.orig./include/dos_inc.h
---/include/dos_inc.h.orig 2015-12-27 12:43:12.000000000-0800
+++/include/dos_inc.h 2015-12-27 11:53:19.000000000-0800
@@-170,7+170,7@@void DOS_BuildUMBChain(bool umb_active,b
bool DOS_linkumbstomchain(Bit16u linkstate);
/*FCB材料*/
-bool DOS_FCBOpen(位16u seg,位16u offset);
+位16U DOS_FCBOpen(位16U seg,位16U偏移);
bool DOS_FCBCreate(位16u seg,位16u offset);
bool DOS_FCBClose(位16u seg,位16u offset);
bool DOS_FCBFindFirst(位16u seg,位16u offset);
diff-up./src/dos/dos_classes.cpp.orig./src/dos/dos_classes.cpp
diff-up./src/dos/dos_files.cpp.orig./src/dos/dos_files.cpp
---/src/dos/dos_files.cpp.orig 2015-12-27 10:08:26.000000000-0800
+++/src/dos/dos_files.cpp 2015-12-27 12:22:17.000000000-0800
@@-964,7+964,7@@bool DOS_fcb创建(位16u seg,位16u off
返回true;
}
-bool DOS_FCBOpen(位16u seg,位16u offset){
+位16U DOS_FCBOpen(位16U seg,位16U偏移量){
DOS_FCB FCB(分段、偏移);
字符短名称[DOS_FCBNAME];位16u句柄;
fcb.GetName(短名称);
@@-972,7+972,7@@bool DOS_FCBOpen(位16u seg,位16u offse
/*首先检查名称是否正确*/
比特8U驱动器;
字符全名[DOS_路径长度];
-如果(!DOS_MakeName(shortname、fullname和drive))返回false;
+如果(!DOS_MakeName(shortname、fullname和drive))返回(Bit16u)false;
/*检查文件是否已打开*/
用于(Bit8u i=0;iSeek(&size,DOS\u SEEK\u END);
-DOS_CloseFile(条目);fcb.GetSeqData(句柄、记录大小);
+fcb.GetSeqData(句柄、记录大小);
+DOS_关闭文件(条目);
比特32U随机=(大小/记录大小);
if(大小%rec_大小)随机++;
fcb.SetRandom(随机);
请编辑问题并添加您正在考虑的硬件和操作系统。问得太晚了32年,FCBs在1983年就过时了。首先使用所有必需的信息初始化an(我相信文档的其他部分中也有这样的示例),然后调用int 21h。