I'm using clock_gettime in a program. I've tried including as well as but neither works. I have also added -lrt to my compiler arguments but still I get the same errors.
This is on
CentOS Linux release 7.2.1511 (Core)
gcc (GCC) 4.8.5 20150623 (Red Hat 4.8.5-4)
GNU ld version 2.23.52.0.1-55.el7 20130226
ldd (GNU libc) 2.17
Compiler output:
gcc -o main packet.c connect.c transport.c accept.c main.c close.c util.c receive.c send.c congestion.c -Wall -g -std=c99 -lrt
util.c: In function ‘millis’:
util.c:42:21: error: storage size of ‘t’ isn’t known
struct timespec t;
^
util.c:43:5: warning: implicit declaration of function ‘clock_gettime’ [-Wimplicit-function-declaration]
clock_gettime(CLOCK_MONOTONIC_RAW, &t);
^
util.c:43:19: error: ‘CLOCK_MONOTONIC_RAW’ undeclared (first use in this function)
clock_gettime(CLOCK_MONOTONIC_RAW, &t);
^
Makefile
CFLAGS = -Wall -g -std=c99
LIBS = -lrt
# Should be equivalent to your list of C files, if you don't build selectively
SRC=$(wildcard *.c)
main: $(SRC)
gcc -o $# $^ $(CFLAGS) $(LIBS)
Top of util.h
#ifndef UTILS_438_H_
#define UTILS_438_H_
#include "const.h"
#include "data.h"
#include "transport.h"
#include <time.h>
Top of util.c
#include "util.h"
#include <time.h>
#include <stdio.h>
#include <string.h>
Please let me know if I can supply more information to help answer this
Before including the header(<time.h>), do
#define _POSIX_C_SOURCE 199309L
http://man7.org/linux/man-pages/man2/clock_gettime.2.html
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
clock_getres(), clock_gettime(), clock_settime():
_POSIX_C_SOURCE >= 199309L
http://man7.org/linux/man-pages/man7/feature_test_macros.7.html
_POSIX_C_SOURCE
Defining this macro causes header files to expose definitions as
follows:
· The value 1 exposes definitions conforming to POSIX.1-1990 and
ISO C (1990).
· The value 2 or greater additionally exposes definitions for
POSIX.2-1992.
· The value 199309L or greater additionally exposes definitions
for POSIX.1b (real-time extensions).
· The value 199506L or greater additionally exposes definitions
for POSIX.1c (threads).
· (Since glibc 2.3.3) The value 200112L or greater additionally
exposes definitions corresponding to the POSIX.1-2001 base
specification (excluding the XSI extension). This value also
causes C95 (since glibc 2.12) and C99 (since glibc 2.10)
features to be exposed (in other words, the equivalent of
defining _ISOC99_SOURCE).
· (Since glibc 2.10) The value 200809L or greater additionally
exposes definitions corresponding to the POSIX.1-2008 base
specification (excluding the XSI extension).
Simply replace -std=c99 with -std=gnu99.
Thisway you do not have to add _POSIX_C_SOURCE
if you can use the following linker and Compiler flags
CFLAGS = -g -Wall -std=c99 -D_POSIX_SOURCE -D_GNU_SOURCE
LDFLAGS = -lpthread -lrt
you can get the build done in the Linux systems. -lrt linker and -D_POSIX_SOURCE are the important ones
Related
I'm trying to measure the amount of time an operation is taking, as accurately as possible. My research led me to believe that clock_gettime() and friends is what I want.
However, I can't for the life of me get it to work. Consider this seemingly trivial example:
#include <time.h>
#include <unistd.h>
int main(void)
{
struct timespec t;
clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &t);
return 0;
}
If I run that through the preprocessor, everything looks like it's just fine:
$ cpp time.c | tail -n10
# 1163 "/usr/include/unistd.h" 3 4
# 3 "time.c" 2
int main(void)
{
struct timespec t;
clock_gettime(2, &t);
return 0;
}
However, if I try to compile the preprocessed code, it won't:
$ cpp time.c > time-prep.c
$ cc -o time -Wall -std=c11 -lrt time-prep.c
/tmp/user/1000/cc00SdhB.o: In function `main':
time-prep.c:(.text+0x15): undefined reference to `clock_gettime'
collect2: error: ld returned 1 exit status
$
If I try to compile the original, it doesn't go any better:
$ cc -o time -Wall -std=c11 -lrt time.c
time.c: In function ‘main’:
time.c:6:18: error: storage size of ‘t’ isn’t known
time.c:7:2: warning: implicit declaration of function ‘clock_gettime’ [-Wimplicit-function-declaration]
time.c:7:16: error: ‘CLOCK_PROCESS_CPUTIME_ID’ undeclared (first use in this function)
time.c:7:16: note: each undeclared identifier is reported only once for each function it appears in
time.c:6:18: warning: unused variable ‘t’ [-Wunused-variable]
$
The man page for clock_gettime says that I need to
Link with -lrt (only for glibc versions before 2.17).
but as you can see, I'm already doing that. Adding or removing -lrt to cc doesn't seem to make any difference whatsoever in my case.
I have looked at /usr/include/time.h but don't see anything obvious that I am missing.
What (presumably trivial) incantation is missing for me to be able to use clock_gettime() in my code?
The Linux documentation for clock_gettime() specifies a feature-test requirement:
_POSIX_C_SOURCE >= 199309L
You could consider fulfilling that directly, perhaps via a #define directive at the very beginning of your code, since the code in fact does depend on it.
If you do not provide such a #define, then gcc may nevertheless do it for you, depending on the options you specify to it. By default, it will do. Likewise with -std=gnu99 or -std=gnu11. But you attempted to compile with -std=c11, which asks for strict(ish) compliance with C11. C11 does not define the needed POSIX feature-test macro.
You can define _GNU_SOURCE above any #include. There is an example:
$cat ./main.c
// Need for clock_gettime()
// Have to be at the begining of the file
#define _GNU_SOURCE
#include <time.h>
#include <unistd.h>
int main(void)
{
...
}
I am trying to compile timersub() function in linux but i always get:
test.c: In function ‘main’:
test.c:27:2: warning: implicit declaration of function ‘timersub’ [-Wimplicit-function-declaration]
timersub(&now, &then, &diff);
^
/tmp/ccLzfLsl.o: In function `main':
test.c:(.text+0x55): undefined reference to `timersub'
collect2: error: ld returned 1 exit status
this is just a simple code of the function with all the library that i use..
#define _XOPEN_SOURCE
#define _POSIX_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <sys/time.h>
#include "openflow.h"
#include "cbench.h"
#include "fakeswitch.h"
#include <unistd.h>
int main()
{
struct timeval now, then, diff;
gettimeofday(&then,NULL);
sleep(1);
gettimeofday(&now, NULL);
timersub(&now, &then, &diff);
return 0;
}
i am compiling it with:
gcc --std=c99 -Wall -DTRACE -o test test.c
See the manual. It's not in POSIX but in BSD function. So you need _BSD_SOURCE.
Define it at the top:
#define _BSD_SOURCE
or alternatively compile with:
gcc --std=c99 -Wall -DTRACE -D_BSD_SOURCE -o test test.c
Since Glibc 2.20, the macro _BSD_SOURCE has been deprecated and has been superseded by _DEFAULT_SOURCE. From feature test macros:
_DEFAULT_SOURCE (since glibc 2.19)
This macro can be defined to
ensure that the "default" definitions are provided even when the
defaults would otherwise be disabled, as happens when individual
macros are explicitly defined, or the compiler is invoked in one of
its "standard" modes (e.g., cc -std=c99). Defining _DEFAULT_SOURCE
without defining other individual macros or invoking the compiler in
one of its "stan‐ dard" modes has no effect.
The "default" definitions comprise those required by POSIX.1-2008 and
ISO C99, as well as various definitions originally derived from BSD
and System V. On glibc 2.19 and earlier, these defaults were
approximately equivalent to explicitly defining the following:
cc -D_BSD_SOURCE -D_SVID_SOURCE -D_POSIX_C_SOURCE=200809
But if you are using an older Gblic, you'd still need to use _BSD_SOURCE.
Basically i just deleted #define _XOPEN_SOURCE and #define _POSIX_SOURCE and compiled it only with gcc -Wall -DTRACE and it worked
I have this code:
#include <string.h>
#include <stdio.h>
char numbers[5] = "12345";
int main(){
memrchr(numbers,'2',5);
for(int i=0;i<5;i++){
printf("%d",i);
}
return 0;
}
It uses for loop inital declarations (for(int i) and gnu extensions (memrchr).
I am using the compiler gcc
The problem is that it doesn't seem to let both go through. I can either do
gcc program.c -o program
Which complains about the for loops, or I can do
gcc -std=gnu11 program.c -o program
Which complains about memrchr being undefined. (or rather it complains about the implicit declaration of the function)
How do I do both? Is it possible?
You need to define the _GNU_SOURCE feature-test macro before any library #include. A convenient way to do that is to put it in your command line:
gcc -std=c11 -D_GNU_SOURCE program.c -o program
Or you could put the #define at the very top of every file which needs it. (Putting them in the source file is probably better, but I've gotten into the habit of putting them in my Makefiles. YMMV.)
You can see the needed feature-test macros in the manpage for every C library function. For example, man memrchr includes:
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
memrchr(), rawmemchr(): _GNU_SOURCE
As that says, man feature_test_macros will tell you more.
I am trying to run a example on handling signals, and it fails compiling on a unfound identifier.
Here is how the header is loaded :
#define __USE_GNU
#include <ucontext.h>
And the error when compiling (with gcc):
$ gcc -o sa_siginfo sa_siginfo.c
sa_siginfo.c: In function ‘bt_sighandler’:
sa_siginfo.c:25:28: error: ‘REG_RIP’ undeclared (first use in this function)
uc->uc_mcontext.gregs[REG_RIP]);
GCC info:
$ gcc --version
gcc (Ubuntu/Linaro 4.8.1-10ubuntu9) 4.8.1
/usr/include/ucontext.h does include /usr/include/sys/ucontext.h which has:
#ifdef __x86_64__
[...]
#ifdef __USE_GNU
/* Number of each register in the `gregset_t' array. */
enum
{
[...]
REG_RIP,
(My system is 64 bits)
So I don't understand why it doesn't find it ?
Try compiling your program like this
gcc -D_GNU_SOURCE -o sa_siginfo sa_siginfo.c
That __USE_GNU is defined only if you defined _GNU_SOURCE, and gcc will not define it by default.
Trying to build vSphere Perl SDK on Centos 2.6. Got all dependencies except one, namely UUID-0.05.
The problem seems to be that the uuid.h include file references unistd.h for the definition of uuid_t, but unistd.h has no such thing. Worse, though some people have described a conflict between the two include files for the variable, I cannot find a unistd.h file on the Internet with the definition.
Can someone point to such a unistd.h file? Or, even, a better approach to take?
Here's some info about the original issue:
In Changelog for uuid.1.6.2:
o Apply workaround to uuid.h to avoid conflicts with
vendor UUID implementations where uuid_t (Darwin/MacOSX)
or uuid_create/uuid_compare (POSIX) might exist.
[Ralf S. Engelschall]
In uuid.h:
/* workaround conflicts with system headers */
#define uuid_t __vendor_uuid_t
#define uuid_create __vendor_uuid_create
#define uuid_compare __vendor_uuid_compare
#include <sys/types.h>
#include <unistd.h>
#undef uuid_t
#undef uuid_create
#undef uuid_compare
Here's the original problem (compiling):
jloiacon#flowviewerprime /home/jloiacon/UUID-0.05 249 >make
cp UUID.pm blib/lib/UUID.pm
/usr/bin/perl /usr/share/perl5/ExtUtils/xsubpp -typemap /usr/share/perl5/ExtUtils/typemap UUID.xs > UUID.xsc && mv UUID.xsc UUID.c
gcc -c -D_REENTRANT -D_GNU_SOURCE -fno-strict-aliasing -pipe -fstack-protector -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 -O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector --param=ssp-buffer-size=4 -m64 -mtune=generic -DVERSION=\"0.05\" -DXS_VERSION=\"0.05\" -fPIC "-I/usr/lib64/perl5/CORE" UUID.c
UUID.xs: In function âdo_generateâ:
UUID.xs:13: error: storage size of âuuidâ isnât known
UUID.xs:14: warning: implicit declaration of function âuuid_generateâ
UUID.xs:13: warning: unused variable âuuidâ
UUID.xs: In function âdo_unparseâ:
UUID.xs:20: error: storage size of âuuidâ isnât known
UUID.xs:23: warning: implicit declaration of function âuuid_unparseâ
UUID.xs:20: warning: unused variable âuuidâ
UUID.xs: In function âdo_parseâ:
UUID.xs:29: error: storage size of âuuidâ isnât known
UUID.xs:33: warning: implicit declaration of function âuuid_parseâ
UUID.xs:30: warning: unused variable âstrâ
UUID.xs:29: warning: unused variable âuuidâ
make: *** [UUID.o] Error 1
Thanks
Install uuid-c++-devel.
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