strlen

Purpose:	Determine the number of BYTEs in an ASCIIz string in SRAM.
Assumes:	The string is between 0 and 2,048 BYTEs in length (which is all available SRAM in a 328P).
Passed:	R25:R24	CHAR *	szBuffer	pointer to the SRAM buffer to examine
Returns:	R25:R24	WORD	wCount	the BYTE count in the ASCIIz string, which may be zero.
	FLAGS	ZERO	flag	set (TRUE) when length is zero (and R25:R24 = 0) OR clear (FALSE) when length is > 0 (and R25:R24 > 0)
Alters:	Only R24, R25 and the FLAGs

Example:	.ORG 0x1000 CheckLength: ADIW R26, 0 ; If 'X' is zero, the command line has nothing BREQ ACheckLength_Ret ; to be checked, so just exit immediately MOVW R24, R26 LDI R22, '"' ; Specify the string starting delimiter BYTE CALL Astrchr ; Search for the first occurrence of a double BREQ ACheckLength_Ret ; quote character; exit if none found ADIW R24, 1 ; Advance to the BYTE after the first double CALL Astrlen ; quote character and get the string length CALL APrintWORD ; Should only need PrintBYTE, but since it LDI R25, ACSZ_BYTEs >> 8 ; suppresses leading zeros, use PrintWORD LDI R24, ACSZ_BYTEs & 0xFF CALL APrintFLASHASCIIz ; This string below, ending in CR, LF CheckLength_Ret: RET CSZ_BYTEs: .STRING " BYTEs in the string\n"
Test it:	m>DF+ 0x1000 64 ; Verify the FLASH memory range is unused FLASH (program memory) contents: 1000: FF FF FF FF FF FF FF FF-FF FF FF FF FF FF FF FF ................ 1010: FF FF FF FF FF FF FF FF-FF FF FF FF FF FF FF FF ................ 1020: FF FF FF FF FF FF FF FF-FF FF FF FF FF FF FF FF ................ 1030: FF FF FF FF FF FF FF FF-FF FF FF FF FF FF FF FF ................ m>:10100000109671F0CD0162E20E941D3049F0019608 m>:101010000E9420300E94543090E182E20E944930C8 m>:10102000089520425954457320696E2074686520E4 m>:08103000737472696E670A0017 m>:00000001FF m>DF+ 0x1000 64 ; Verify that it loaded FLASH (program memory) contents: 1000: 10 96 71 F0 CD 01 62 E2-0E 94 1D 30 49 F0 01 96 ..q...b....0I... 1010: 0E 94 20 30 0E 94 54 30-90 E1 82 E2 0E 94 49 30 .. 0..T0......I0 1020: 08 95 20 42 59 54 45 73-20 69 6E 20 74 68 65 20 .. BYTEs in the 1030: 73 74 72 69 6E 67 0A 00-FF FF FF FF FF FF FF FF string.......... m>@ 0x1000 " 0 BYTEs in the string m>@ 0x1000 "Test 4 BYTEs in the string m>@ 0x1000 "A longer string... 18 BYTEs in the string m>
Notes:	An ASCIIz string is a series of printable characters, the end of which is defined by a NULL (= 0) BYTE.
	The string may begin with a NULL, which is valid and will return zero length. The ZERO flag has already been set or cleared, so no comparison is needed.
Dropin: (setup code)	; Setup for the strlen() call: ; Passed: R25:R24 CHAR * szBuffer pointer to the SRAM buffer to check ; Returns: R25:R24 WORD wCount, number of BYTEs before the first NULL BYTE ; (Also:) ZERO FLAG set (TRUE) when length is zero (and R25:R24 = 0) ; clear (FALSE) when length is > 0 (and R25:R24 > 0) ; Alters: Only R24, R25, and the FLAGs
Also see:	The strcpy, strlenEEPROM, and strlenPGM System Functions.