Can you read or seek from an embedded file?
Sometimes you might want to embed a file inside an exe. For example, if you add a file into a project and don’t mark it as Excluded, the file will be physically inserted inside the target EXE or APP. Visual Class Libraries (VCX files), Forms (SCX files), Reports (FRX) and other files that are not marked as Excluded are also embedded inside. When the user code tries to open a file with the same name as one that’s embedded, the embedded one will be opened. Embedded files cannot be written to, so they need to be opened READONLY.
The code below creates a test file TEST.BIN of 256 bytes and uses the FSEEK() function to seek various positions in the file and read its contents. Then the code embeds the test file into an APP and does the same tests.
When you seek before the start of the file, an error occurs. When you seek past the end of file, no error occurs, but reading from beyond the end of file returns no bytes read. If the read straddles the end of file, then the bytes up to the eof are read. The same behavior must occur whether the file is embedded or not, and whether the file is opened buffered or not.
(The original bug report was from www.FoxClub.ru)
The output is like this:
Pos Mode FSeek ErrCode CurPos AfterRead Read10 bytes
50 0 50 0 50 60 10 50 51 52 53 54 55 56 57 58 59
-15 0 0 25 60 70 10 60 61 62 63 64 65 66 67 68 69
5 1 75 0 75 85 10 75 76 77 78 79 80 81 82 83 84
40 1 125 0 125 135 10 125 126 127 128 129 130 131 132 133 134
-800 1 0 25 135 145 10 135 136 137 138 139 140 141 142 143 144
-55 1 90 0 90 100 10 90 91 92 93 94 95 96 97 98 99
-50 2 206 0 206 216 10 206 207 208 209 210 211 212 213 214 215
-800 2 0 25 216 226 10 216 217 218 219 220 221 222 223 224 225
50 2 306 0 306 306 0
-5 2 251 0 251 256 5 251 252 253 254 0
SET SAFETY OFF
_screen.FontName="Courier new"
LOCAL nHandle
LOCAL cStr
cStr=''
FOR i=0 to 255
cStr=cStr+CHR(MOD(i,256))
ENDFOR
nHandle=FCREATE("test.bin")
FWRITE(nHandle,cStr)
FCLOSE(nHandle)
TEXT TO cstr NOSHOW
PROCEDURE Temp(nOpenmode as Integer) as String
SET ALTERNATE TO temp.txt
SET ALTERNATE ON
?"Open mode = ",nOpenMode
nHandle=FOPEN("test.bin",nOpenmode) && unbuffered, must be readonly for embedded file
IF nHandle=-1
?"Error opening file",FERROR()
ELSE
?" Pos Mode FSeek ErrCode CurPos AfterRead Read10 bytes"
doit(nHandle, 50,0) && seek 50 bytes rel from start
doit(nHandle, -15,0) && seek-15 bytes rel from start: err
doit(nHandle, 5,1) && seek 5 bytes rel from curpos
doit(nHandle, 40,1) && seek 40 bytes rel from curpos
doit(nHandle,-800,1) && seek -800 bytes rel from curpos: err
doit(nHandle, -55,1) && seek -55 bytes rel from curpos
doit(nHandle, -50,2) && seek -50 bytes rel from end
doit(nHandle,-800,2) && seek -800 bytes rel from end : err
doit(nHandle, 50,2) && seek 50 bytes rel from end: no err, none read
doit(nHandle, -5,2) && seek -5 bytes rel from end:partial read
FCLOSE(nHandle)
ENDIF
SET ALTERNATE TO
RETURN FILETOSTR("temp.txt")
PROCEDURE doit(nHandle, npos as Integer, nMode as Integer)
?npos,nMode
??FSEEK(nHandle,npos, nMode)
??FERROR() && 0 = no error
??FSEEK(nHandle,0,1) && Show Cur Pos
cbuf=FREAD(nHandle,10) && Try to read 10 bytes: changes curpos
??FSEEK(nHandle,0,1) && Show cur pos after read
??LEN(cBuf) && Show # bytes read
FOR i = 1 TO MIN(LEN(cBuf),10) && Show up to 10 of the bytes read
??ASC(SUBSTR(cbuf,i,1))
ENDFOR
ENDTEXT
STRTOFILE(cstr,"temp.prg")
COMPILE temp.prg
ERASE temp.app
cresNorm=temp(0)+temp(10)
BUILD PROJECT temp FROM temp
MODIFY PROJECT temp nowait
_vfp.ActiveProject.Files.Add("test.bin") && embed the generated binary file
_vfp.ActiveProject.Close
BUILD APP temp FROM temp
ERASE temp.prg
ERASE temp.fxp
?"Now embedded"
cresEmbed=temp(0)+temp(10)
?"Are they equal?",cresEmbed==cresNorm
RETURN