>Synopsis: SCNuFASTx and SCNdFASTx macros from inttypes.h does not work
>for x < 32
>Category: user
>Environment:
System : OpenBSD 6.4
Details : OpenBSD 6.4-current (GENERIC.MP) #462: Wed Nov 21
22:23:22 MST 2018
[email protected]:/usr/src/sys/arch/amd64/compile/GENERIC.MP
Architecture: OpenBSD.amd64
Machine : amd64
>Description:
When using scanf() to read a value into a uint_fast8_t or uint_fast16_t
variable (or the signed equivalent), there is a mismatch between the
type of the variable and the format specification that the corresponding
SCN{u,d}FAST{8,16} macro expands to.
This seems to affect the {u,}int_fast{8,16}_t types and not the "least"
variant or ordinary {u,}int{8,16}_t types.
This gives rise to warnings from clang, and also affects the values that
are stored in the variables (see below).
The actual warning from clang (see code further down too):
prog.c:16:19: warning: format specifies type 'unsigned short *' but the
argument has type 'uint_fast16_t *' (aka 'unsigned int *') [-Wformat]
&a, &b, &c) != 3) {
^~
prog.c:16:23: warning: format specifies type 'unsigned char *' but the argument
has type 'uint_fast8_t *' (aka 'unsigned int *') [-Wformat]
&a, &b, &c) != 3) {
^~
2 warnings generated.
>How-To-Repeat:
Compile the below program using "cc -std=c99 prog.c"
#include <inttypes.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
int
main(void)
{
uint_fast32_t a;
uint_fast16_t b;
uint_fast8_t c;
if (scanf("%" SCNuFAST32
" %" SCNuFAST16
" %" SCNuFAST8,
&a, &b, &c) != 3) {
fputs("Failed in scanf\n", stderr);
exit(EXIT_FAILURE);
}
printf("a\t= %" PRIuFAST32 "\n", a);
printf("b\t= %" PRIuFAST16 "\n", b);
printf("c\t= %" PRIuFAST8 "\n", c);
return EXIT_SUCCESS;
}
Note also that the b value (uint_fast16_t) is read incorrectly:
$ echo "1 2 3" | ./a.out
a = 1
b = 1324285954
c = 3
Also note that using the signed types int_fast{8,16}_t and the
SCNdFAST{8,16}, the same issue is present, and additionally, the c value
(int_fast8_t) is read incorrectly if negative (but not if a positive
value is entered):
$ echo "-1 -2 -3" | ./a.out
a = -1
b = -1450967042
c = 253
I'd be very happy to have errors in my code relating to the use of the
SCN macros pointed out to me.
>Fix:
Unknown.
dmesg:
OpenBSD 6.4-current (GENERIC.MP) #462: Wed Nov 21 22:23:22 MST 2018
[email protected]:/usr/src/sys/arch/amd64/compile/GENERIC.MP
real mem = 4278124544 (4079MB)
avail mem = 4139184128 (3947MB)
mpath0 at root
scsibus0 at mpath0: 256 targets
mainbus0 at root
bios0 at mainbus0: SMBIOS rev. 2.5 @ 0xe1000 (10 entries)
bios0: vendor innotek GmbH version "VirtualBox" date 12/01/2006
bios0: innotek GmbH VirtualBox
acpi0 at bios0: rev 2
acpi0: sleep states S0 S5
acpi0: tables DSDT FACP APIC SSDT
acpi0: wakeup devices
acpitimer0 at acpi0: 3579545 Hz, 32 bits
acpimadt0 at acpi0 addr 0xfee00000: PC-AT compat
cpu0 at mainbus0: apid 0 (boot processor)
cpu0: Intel(R) Core(TM) i5-4570 CPU @ 3.20GHz, 3512.37 MHz, 06-3c-03
cpu0:
FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,APIC,SEP,MTRR,PGE,MCA,CMOV,PAT,PSE36,CFLUSH,MMX,FXSR,SSE,SSE2,HTT,SSE3,PCLMUL,SSSE3,CX16,PCID,SSE4.1,SSE4.2,MOVBE,POPCNT,AES,XSAVE,AVX,RDRAND,NXE,RDTSCP,LONG,LAHF,ABM,ITSC,FSGSBASE,AVX2,INVPCID,L1DF,MELTDOWN
cpu0: 256KB 64b/line 8-way L2 cache
cpu0: smt 0, core 0, package 0
mtrr: CPU supports MTRRs but not enabled by BIOS
cpu0: apic clock running at 1010MHz
cpu1 at mainbus0: apid 1 (application processor)
cpu1: Intel(R) Core(TM) i5-4570 CPU @ 3.20GHz, 3224.88 MHz, 06-3c-03
cpu1:
FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,APIC,SEP,MTRR,PGE,MCA,CMOV,PAT,PSE36,CFLUSH,MMX,FXSR,SSE,SSE2,HTT,SSE3,PCLMUL,SSSE3,CX16,PCID,SSE4.1,SSE4.2,MOVBE,POPCNT,AES,XSAVE,AVX,RDRAND,NXE,RDTSCP,LONG,LAHF,ABM,ITSC,FSGSBASE,AVX2,INVPCID,L1DF,MELTDOWN
cpu1: 256KB 64b/line 8-way L2 cache
cpu1: smt 0, core 1, package 0
ioapic0 at mainbus0: apid 2 pa 0xfec00000, version 20, 24 pins, remapped
acpiprt0 at acpi0: bus 0 (PCI0)
acpicpu0 at acpi0: C1(@1 halt!)
acpicpu1 at acpi0: C1(@1 halt!)
acpipci0 at acpi0 PCI0: 0x00000000 0x00000011 0x00000001
acpiac0 at acpi0: AC unit online
acpivideo0 at acpi0: GFX0
pci0 at mainbus0 bus 0
pchb0 at pci0 dev 0 function 0 "Intel 82441FX" rev 0x02
pcib0 at pci0 dev 1 function 0 "Intel 82371SB ISA" rev 0x00
pciide0 at pci0 dev 1 function 1 "Intel 82371AB IDE" rev 0x01: DMA, channel 0
configured to compatibility, channel 1 configured to compatibility
wd0 at pciide0 channel 0 drive 0: <VBOX HARDDISK>
wd0: 128-sector PIO, LBA, 102400MB, 209715200 sectors
atapiscsi0 at pciide0 channel 0 drive 1
scsibus1 at atapiscsi0: 2 targets
cd0 at scsibus1 targ 0 lun 0: <VBOX, CD-ROM, 1.0> ATAPI 5/cdrom removable
wd0(pciide0:0:0): using PIO mode 4, Ultra-DMA mode 2
cd0(pciide0:0:1): using PIO mode 4, Ultra-DMA mode 2
wd1 at pciide0 channel 1 drive 0: <VBOX HARDDISK>
wd1: 128-sector PIO, LBA, 5120MB, 10485760 sectors
wd1(pciide0:1:0): using PIO mode 4, Ultra-DMA mode 2
vga1 at pci0 dev 2 function 0 "InnoTek VirtualBox Graphics Adapter" rev 0x00
wsdisplay0 at vga1 mux 1: console (80x25, vt100 emulation)
wsdisplay0: screen 1-5 added (80x25, vt100 emulation)
virtio0 at pci0 dev 3 function 0 "Qumranet Virtio Network" rev 0x00
vio0 at virtio0: address 08:00:27:4c:c3:b6
virtio0: apic 2 int 19
"InnoTek VirtualBox Guest Service" rev 0x00 at pci0 dev 4 function 0 not
configured
piixpm0 at pci0 dev 7 function 0 "Intel 82371AB Power" rev 0x08: apic 2 int 23
iic0 at piixpm0
virtio1 at pci0 dev 8 function 0 "Qumranet Virtio Network" rev 0x00
vio1 at virtio1: address 08:00:27:56:79:c2
virtio1: apic 2 int 16
isa0 at pcib0
isadma0 at isa0
pckbc0 at isa0 port 0x60/5 irq 1 irq 12
pckbd0 at pckbc0 (kbd slot)
wskbd0 at pckbd0: console keyboard, using wsdisplay0
pms0 at pckbc0 (aux slot)
wsmouse0 at pms0 mux 0
pcppi0 at isa0 port 0x61
spkr0 at pcppi0
vscsi0 at root
scsibus2 at vscsi0: 256 targets
softraid0 at root
scsibus3 at softraid0: 256 targets
root on wd0a (411f6d6665fa8a05.a) swap on wd0b dump on wd0b
usbdevs:
usbdevs: no USB controllers found
--
Andreas Kusalananda Kähäri,
National Bioinformatics Infrastructure Sweden (NBIS),
Uppsala University, Sweden.
