I wonder if it is possible to get it compiled for use in a DOS application.

Here's a much older version:

https://www.ibiblio.org/pub/micro/pc-stuff/freedos/files/distributions/1.2/repos/pkg-html/sqlite.html

Good luck getting a halfway recent one to build.

FYI , Tom:

• http://www.win3x.org forum thread
• SQLite 3.46.1 for DOS + reference

a DOS application

What is a DOS application? Do you mean SQLite3.EXE compiled as a 16-bit executable?

Look like Tom was meant exactly SQLite3.EXE compiled as a 16-bit or 32-bit executable for DOS.

Adopted SQLite 3.46.1 for DOS based on some tiny code changes and Tcl script. Thanks to Ben Collver!

I hope this 2 files ( Makefile.cross-djgpp-tcl90 and sqlite-3.46.1-djgpp.diff ) will be usefully for SQLite and DOS communities for future SQLite versions.

sqlite-3.46.1-djgpp.diff

diff -Pur sqlite-src-3460100-orig/src/os_unix.c sqlite-src-3460100/src/os_unix.c
--- sqlite-src-3460100-orig/src/os_unix.c	2024-10-08 14:03:37.579253663 -0700
+++ sqlite-src-3460100/src/os_unix.c	2024-10-08 14:03:53.168253202 -0700
@@ -411,7 +411,9 @@
 
 /* Forward reference */
 static int openDirectory(const char*, int*);
+#if LINUX == 1
 static int unixGetpagesize(void);
+#endif
 
 /*
 ** Many system calls are accessed through pointer-to-functions so that
@@ -445,7 +447,7 @@
 ** that always succeeds.  This means that locking does not occur under
 ** DJGPP.  But it is DOS - what did you expect?
 */
-#ifdef __DJGPP__
+#ifdef __DDJGPP__
   { "fstat",        0,                 0  },
 #define osFstat(a,b,c)    0
 #else   
@@ -456,8 +458,13 @@
   { "ftruncate",    (sqlite3_syscall_ptr)ftruncate,  0  },
 #define osFtruncate ((int(*)(int,off_t))aSyscall[6].pCurrent)
 
+#ifdef __DJGPP__
+  { "fcntl",        0,                 0  },
+#define osFcntl(a,b,c)    0
+#else
   { "fcntl",        (sqlite3_syscall_ptr)fcntl,      0  },
 #define osFcntl     ((int(*)(int,int,...))aSyscall[7].pCurrent)
+#endif
 
   { "read",         (sqlite3_syscall_ptr)read,       0  },
 #define osRead      ((ssize_t(*)(int,void*,size_t))aSyscall[8].pCurrent)
@@ -915,7 +922,9 @@
   switch (posixError) {
   case EACCES:
   case EAGAIN:
+#ifndef __DJGPP__
   case ETIMEDOUT:
+#endif
   case EBUSY:
   case EINTR:
   case ENOLCK:
@@ -1502,6 +1511,10 @@
 ** Return TRUE if pFile has been renamed or unlinked since it was first opened.
 */
 static int fileHasMoved(unixFile *pFile){
+#ifdef __DJGPP__
+  // this check returns 'true' in DJGPP enviroments even if the file was not moved --> don't check
+  return 0;
+#else
 #if OS_VXWORKS
   return pFile->pInode!=0 && pFile->pId!=pFile->pInode->fileId.pId;
 #else
@@ -1510,6 +1523,7 @@
       (osStat(pFile->zPath, &buf)!=0
          || (u64)buf.st_ino!=pFile->pInode->fileId.ino);
 #endif
+#endif
 }
 
 
@@ -1613,7 +1627,21 @@
 ** attempt to set the lock.
 */
 #ifndef SQLITE_ENABLE_SETLK_TIMEOUT
+#ifdef __DJGPP__
+//# define osSetPosixAdvisoryLock(h,x,t) 0
+static inline int osSetPosixAdvisoryLock(
+  int h,                /* The file descriptor on which to take the lock */
+  struct flock *pLock,  /* The description of the lock */
+  unixFile *pFile       /* Structure holding timeout value */
+){
+  ((void)h);
+  ((void)pLock);
+  ((void)pFile);
+  return 0;
+}
+#else
 # define osSetPosixAdvisoryLock(h,x,t) osFcntl(h,F_SETLK,x)
+#endif
 #else
 static int osSetPosixAdvisoryLock(
   int h,                /* The file descriptor on which to take the lock */
@@ -6734,6 +6762,11 @@
   }
   appendAllPathElements(&path, zPath);
   zOut[path.nUsed] = 0;
+#ifdef __DJGPP__
+  if (zOut[0] == '/' && zOut[2] == ':') {
+    memmove(zOut, &zOut[1], path.nUsed);
+  }
+#endif
   if( path.rc || path.nUsed<2 ) return SQLITE_CANTOPEN_BKPT;
   if( path.nSymlink ) return SQLITE_OK_SYMLINK;
   return SQLITE_OK;

Makefile.cross-djgpp-tcl90

#!/usr/make
#
# Makefile for SQLITE
#
# This is a template makefile for SQLite.  Most people prefer to
# use the autoconf generated "configure" script to generate the
# makefile automatically.  But that does not work for everybody
# and in every situation.  If you are having problems with the
# "configure" script, you might want to try this makefile as an
# alternative.  Create a copy of this file, edit the parameters
# below and type "make".
#

#### The toplevel directory of the source tree.  This is the directory
#    that contains this "Makefile.in" and the "configure.in" script.
#
TOP = .

#### C Compiler and options for use in building executables that
#    will run on the platform that is doing the build.
#
BCC = gcc -g -O0
#BCC = /opt/ancic/bin/c89 -0

#### If the target operating system supports the "usleep()" system
#    call, then define the HAVE_USLEEP macro for all C modules.
#
#USLEEP = 
USLEEP = -DHAVE_USLEEP=1

#### If you want the SQLite library to be safe for use within a 
#    multi-threaded program, then define the following macro
#    appropriately:
#
#THREADSAFE = -DTHREADSAFE=1
THREADSAFE = -DTHREADSAFE=0

#### Specify any extra linker options needed to make the library
#    thread safe
#
#THREADLIB = -lpthread -lm -ldl
THREADLIB = 

#### Specify any extra libraries needed to access required functions.
#
#TLIBS = -lrt    # fdatasync on Solaris 8
TLIBS = 

#### Leave SQLITE_DEBUG undefined for maximum speed.  Use SQLITE_DEBUG=1
#    to check for memory leaks.  Use SQLITE_DEBUG=2 to print a log of all
#    malloc()s and free()s in order to track down memory leaks.
#    
#    SQLite uses some expensive assert() statements in the inner loop.
#    You can make the library go almost twice as fast if you compile
#    with -DNDEBUG=1
#
#OPTS += -DSQLITE_DEBUG=1
#OPTS += -DSQLITE_ENABLE_WHERETRACE
#OPTS += -DSQLITE_ENABLE_SELECTTRACE
OPTS = -DNDEBUG=1
OPTS += -DHAVE_NANOSLEEP=0
OPTS += -DSQLITE_ENABLE_8_3_NAMES=2
OPTS += -DSQLITE_ENABLE_FTS5=1
OPTS += -DSQLITE_ENABLE_JSON1=1
OPTS += -DSQLITE_ENABLE_LOCKING_STYLE=0
OPTS += -DSQLITE_DEFAULT_MEMSTATUS=0
OPTS += -DSQLITE_MAX_MMAP_SIZE=0
OPTS += -DSQLITE_NO_SYNC=1
OPTS += -DSQLITE_OMIT_WAL=1
OPTS += -DSQLITE_THREADSAFE=0

#### The suffix to add to executable files.  ".exe" for windows.
#    Nothing for unix.
#
EXE = .exe
#EXE =

#### C Compile and options for use in building executables that 
#    will run on the target platform.  This is usually the same
#    as BCC, unless you are cross-compiling.
#
TCC = /home/ben/local/cross-djgpp/bin/i586-pc-msdosdjgpp-gcc -O6
#TCC = gcc -g -O0 -Wall
#TCC = gcc -g -O0 -Wall -fprofile-arcs -ftest-coverage
#TCC = /opt/mingw/bin/i386-mingw32-gcc -O6
#TCC = /opt/ansic/bin/c89 -O +z -Wl,-a,archive

#### Tools used to build a static library.
#
AR = /home/ben/local/cross-djgpp/bin/i586-pc-msdosdjgpp-ar cr
#AR = /opt/mingw/bin/i386-mingw32-ar cr
RANLIB = ranlib
#RANLIB = /opt/mingw/bin/i386-mingw32-ranlib

MKSHLIB = /home/ben/local/cross-djgpp/bin/i586-pc-msdosdjgpp-gcc -shared
SO = so
SHPREFIX = lib
# SO = dll
# SHPREFIX =

#### Extra compiler options needed for programs that use the TCL library.
#
#TCL_FLAGS = -I/home/drh/tcl/include/tcl8.6
TCL_FLAGS = -I/home/ben/local/tcl9.0.0/generic -DSTATIC_BUILD=1 -DCONST=const -DTCL_CHANNEL_VERSION_2=TCL_CHANNEL_VERSION_5

#### Linker options needed to link against the TCL library.
#
#LIBTCL = -ltcl -lm -ldl
LIBTCL = /home/drh/tcl/lib/libtcl9.0.a -lm -lpthread -ldl -lz

#### Additional objects for SQLite library when TCL support is enabled.
#LIBOBJ =
LIBOBJ = tclsqlite.o

#### Compiler options needed for programs that use the readline() library.
#
READLINE_FLAGS =
#READLINE_FLAGS = -DHAVE_READLINE=1 -I/usr/include/readline

#### Linker options needed by programs using readline() must link against.
#
LIBREADLINE =
#LIBREADLINE = -static -lreadline -ltermcap

# You should not have to change anything below this line
###############################################################################
include $(TOP)/main.mk

Curiously, 3.48.0—which was released 5 days ago—removes the TCL requirement.

Not exactly: it still needs TCL but it now embeds a copy of JimTCL, which, though lighter-weight than full TCL, is sufficient for the project's code-generation needs. Canonical TCL is still required for running the tests.