error: implicit declaration of function 'strtok_r' - linux

Question

I am a newbie in Linux programming (Linux 3.7.10). I tried to compile a program that I got for github but run in to problems with the error. The main program is from ntop where I downloaded the ndpi (https://svn.ntop.org/svn/ntop/trunk/nDPI/) and that compiled ok. The second part is the kernel mode filter that I got from github (https://github.com/ewildgoose/ndpi-netfilter).
First, I could not locate strtok_r function declared in any of the header files. I searched the whole system, is it a prebuild function with in the system?. Please any pointers would be highly appreciated. Thanks.
CC [M] /home/mtot/ndpi/ndpi-netfilter/src/ndpi_cpy/lib/protocols/http.o
/home/mtot/ndpi/ndpi-netfilter/src/ndpi_cpy/lib/protocols/http.c: In function 'check_content_type_and_change_protocol':
/home/mtot/ndpi/ndpi-netfilter/src/ndpi_cpy/lib/protocols/http.c:610:4: error: implicit declaration of function 'strtok_r' [-Werror=implicit-function-declaration]
/home/mtot/ndpi/ndpi-netfilter/src/ndpi_cpy/lib/protocols/http.c:610:10: warning: assignment makes pointer from integer without a cast [enabled by default]
/home/mtot/ndpi/ndpi-netfilter/src/ndpi_cpy/lib/protocols/http.c:617:14: warning: assignment makes pointer from integer without a cast [enabled by default]
/home/mtot/ndpi/ndpi-netfilter/src/ndpi_cpy/lib/protocols/http.c:623:9: warning: assignment makes pointer from integer without a cast [enabled by default]
/home/mtot/ndpi/ndpi-netfilter/src/ndpi_cpy/lib/protocols/http.c:627:11: warning: assignment makes pointer from integer without a cast [enabled by default]
/home/mtot/ndpi/ndpi-netfilter/src/ndpi_cpy/lib/protocols/http.c:632:13: warning: assignment makes pointer from integer without a cast [enabled by default]
cc1: some warnings being treated as errors
make[2]: *** [/home/mtot/ndpi/ndpi-netfilter/src/ndpi_cpy/lib/protocols/http.o] Error 1
make[1]: *** [_module_/home/mtot/ndpi/ndpi-netfilter/src] Error 2
Adding more details
I have located the string.h that has the strtok_r in the /usr/include. What I did was to add the in the http.c file and also the -I/usr/include in the ccflags-y in the Makefile. I got the following errors. Help really needed. Thanks.
CC [M] /home/mtot/ndpi/ndpi-netfilter/src/ndpi_cpy/lib/protocols/http.o
In file included from include/linux/compiler.h:48:0,
from include/uapi/linux/stddef.h:1,
`enter code here` from include/linux/stddef.h:4,
from /usr/src/linux-3.7.10/include/uapi/linux/posix_types.h:4,
from include/uapi/linux/types.h:13,
from include/linux/types.h:5,
from include/uapi/linux/byteorder/little_endian.h:11,
from include/linux/byteorder/little_endian.h:4,
from /usr/src/linux-3.7.10/arch/x86/include/asm/byteorder.h:4,
from /home/mtot/ndpi/ndpi-netfilter/src/ndpi_cpy/include/ndpi_main.h:49,
from /home/mtot/ndpi/ndpi-netfilter/src/ndpi_cpy/include/ndpi_protocols.h:29,
from /home/mtot/ndpi/ndpi-netfilter/src/ndpi_cpy/lib/protocols/http.c:25:
include/linux/compiler-gcc.h:93:0: warning: "__attribute_const__" redefined [enabled by default]
In file included from /usr/include/features.h:375:0,
from /usr/include/string.h:25,
from /home/mtot/ndpi/ndpi-netfilter/src/ndpi_cpy/lib/protocols/http.c:24:
/usr/include/sys/cdefs.h:237:0: note: this is the location of the previous definition
In file included from include/linux/compiler.h:48:0,
from include/uapi/linux/stddef.h:1,
from include/linux/stddef.h:4,
from /usr/src/linux-3.7.10/include/uapi/linux/posix_types.h:4,
from include/uapi/linux/types.h:13,
from include/linux/types.h:5,
from include/uapi/linux/byteorder/little_endian.h:11,
from include/linux/byteorder/little_endian.h:4,
from /usr/src/linux-3.7.10/arch/x86/include/asm/byteorder.h:4,
from /home/mtot/ndpi/ndpi-netfilter/src/ndpi_cpy/include/ndpi_main.h:49,
from /home/mtot/ndpi/ndpi-netfilter/src/ndpi_cpy/include/ndpi_protocols.h:29,
from /home/mtot/ndpi/ndpi-netfilter/src/ndpi_cpy/lib/protocols/http.c:25:
include/linux/compiler-gcc.h:112:0: warning: "__always_inline" redefined [enabled by default]
In file included from /usr/include/features.h:375:0,
from /usr/include/string.h:25,
from /home/mtot/ndpi/ndpi-netfilter/src/ndpi_cpy/lib/protocols/http.c:24:
/usr/include/sys/cdefs.h:308:0: note: this is the location of the previous definition
In file included from include/linux/bitops.h:22:0,
from include/linux/kernel.h:10,
from include/linux/skbuff.h:17,
from include/linux/ip.h:20,
from /home/mtot/ndpi/ndpi-netfilter/src/ndpi_cpy/include/ndpi_main.h:105,
from /home/mtot/ndpi/ndpi-netfilter/src/ndpi_cpy/include/ndpi_protocols.h:29,
from /home/mtot/ndpi/ndpi-netfilter/src/ndpi_cpy/lib/protocols/http.c:25:
/usr/src/linux-3.7.10/arch/x86/include/asm/bitops.h:406:19: error: static declaration of 'ffs' follows non-static declaration
In file included from /usr/src/linux-3.7.10/arch/x86/include/asm/string.h:4:0,
from include/linux/string.h:17,
from include/linux/bitmap.h:8,
from include/linux/cpumask.h:11,
from /usr/src/linux-3.7.10/arch/x86/include/asm/cpumask.h:4,
from /usr/src/linux-3.7.10/arch/x86/include/asm/msr.h:18,
from /usr/src/linux-3.7.10/arch/x86/include/asm/processor.h:20,
from /usr/src/linux-3.7.10/arch/x86/include/asm/thread_info.h:22,
from include/linux/thread_info.h:54,
from include/linux/preempt.h:9,
from include/linux/spinlock.h:50,
from include/linux/mm_types.h:8,
from include/linux/kmemcheck.h:4,
from include/linux/skbuff.h:18,
from include/linux/ip.h:20,
from /home/mtot/ndpi/ndpi-netfilter/src/ndpi_cpy/include/ndpi_main.h:105,
from /home/mtot/ndpi/ndpi-netfilter/src/ndpi_cpy/include/ndpi_protocols.h:29,
from /home/mtot/ndpi/ndpi-netfilter/src/ndpi_cpy/lib/protocols/http.c:25:
/usr/src/linux-3.7.10/arch/x86/include/asm/string_64.h:64:5: error: expected identifier or '(' before '__extension__'
/usr/src/linux-3.7.10/arch/x86/include/asm/string_64.h:64:5: error: expected identifier or '(' before ')' token
In file included from include/linux/bitmap.h:8:0,
from include/linux/cpumask.h:11,
from /usr/src/linux-3.7.10/arch/x86/include/asm/cpumask.h:4,
from /usr/src/linux-3.7.10/arch/x86/include/asm/msr.h:18,
from /usr/src/linux-3.7.10/arch/x86/include/asm/processor.h:20,
from /usr/src/linux-3.7.10/arch/x86/include/asm/thread_info.h:22,
from include/linux/thread_info.h:54,
from include/linux/preempt.h:9,
from include/linux/spinlock.h:50,
from include/linux/mm_types.h:8,
from include/linux/kmemcheck.h:4,
from include/linux/skbuff.h:18,
from include/linux/ip.h:20,
from /home/mtot/ndpi/ndpi-netfilter/src/ndpi_cpy/include/ndpi_main.h:105,
from /home/mtot/ndpi/ndpi-netfilter/src/ndpi_cpy/include/ndpi_protocols.h:29,
from /home/mtot/ndpi/ndpi-netfilter/src/ndpi_cpy/lib/protocols/http.c:25:
include/linux/string.h:38:12: error: expected identifier or '(' before '__extension__'
include/linux/string.h:38:12: error: expected identifier or '(' before ')' token
include/linux/string.h:41:12: error: expected identifier or '(' before '__extension__'
include/linux/string.h:53:15: error: expected identifier or '(' before '__extension__'
include/linux/string.h:83:15: error: expected identifier or '(' before '__extension__'
include/linux/string.h:83:15: error: expected identifier or '(' before ')' token
include/linux/string.h:86:15: error: expected identifier or '(' before '__extension__'
include/linux/string.h:86:15: error: expected identifier or '(' before ')' token
include/linux/string.h:89:24: error: expected identifier or '(' before '__extension__'
include/linux/string.h:89:24: error: expected identifier or '(' before ')' token
include/linux/string.h:92:24: error: expected identifier or '(' before '__extension__'
include/linux/string.h:92:24: error: expected identifier or '(' before ')' token
make[2]: *** [/home/mtot/ndpi/ndpi-netfilter/src/ndpi_cpy/lib/protocols/http.o] Error 1
make[1]: *** [_module_/home/mtot/ndpi/ndpi-netfilter/src] Error 2
make[1]: Leaving directory `/usr/src/linux-3.7.10'
make: *** [all] Error 2
-----MakeFile
NDPI_PATH2 := ${NDPI_PATH}/src
NDPI_SRC := ndpi_cpy
NDPI_PRO := ${NDPI_SRC}/lib/protocols
NDPI_THIRD := $(NDPI_SRC)/lib/third_party/src
SYS_HDR := /usr/include
ccflags-y += -I${src}/${NDPI_SRC}/include -I${src}/${NDPI_SRC}/lib -I${src}/${NDPI_SRC}/lib/third_party/include -I${SYS_HDR} -DOPENDPI_NETFILTER_MODULE
EXTRA_CFLAGS := $(ccflags-y)
#MODULES_DIR := /lib/modules/$(shell uname -r)
#KERNEL_DIR := ${MODULES_DIR}/build
obj-m := xt_ndpi.o
xt_ndpi-y := main.o \
${NDPI_SRC}/lib/ndpi_main.o \
${NDPI_THIRD}/ahocorasick.o \
${NDPI_THIRD}/node.o \
${NDPI_THIRD}/sort.o \
${NDPI_PRO}/afp.o \
${NDPI_PRO}/http.o
all:
if test -d ${NDPI_SRC}; then \
cp ${NDPI_PATH2}/* ${NDPI_SRC} -R; \
else \
mkdir ${NDPI_SRC}; \
cp ${NDPI_PATH2}/* ${NDPI_SRC} -R; \
fi
make -C ${KERNEL_DIR} M=$$PWD;
rm -r ${NDPI_SRC}
modules:
make -C ${KERNEL_DIR} M=$$PWD $#;
modules_install:
make -C ${KERNEL_DIR} M=$$PWD $#;
depmod -a;
clean:
make -C ${KERNEL_DIR} M=$$PWD $#;

Answer 1

strtok_r is typically in string.h. On a Linux system with man-pages installed you can do
man strtok_r
and that will give the manual page:
STRTOK(3) Linux Programmer’s Manual STRTOK(3)
NAME
strtok, strtok_r - extract tokens from strings
SYNOPSIS
#include <string.h>
char *strtok(char *str, const char *delim);
char *strtok_r(char *str, const char *delim, char **saveptr);
...
The include line tells you which file it is in (and must include in your code that uses it). Have you checked to see if you have string.h on your system? It is typically under /usr/include.
A lot of distributions have development packages, have you installed such packages to gain a fully development environment?

Answer 2

Type
man strtok_r
in a terminal. You should get a man page like strtok_r(3) (please follow that link).
Be sure to have installed the appropriate development and documentation packages like libc6-dev (or libc-dev), glibc-doc, manpages-dev. (The actual name depends upon the distribution).