可能重复：
sem_open（）错误：“对sem_open（）的未定义引用”在linux上（Ubuntu 10.10）
posix信号量的编译有问题。我的目标是创建一个共享内存段，并通过信号量来保护它。共享内存运行良好，但信号量代码会给我带来编译错误，即使我包含了信号量.h并在编译标志中添加了-lrt
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <errno.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <semaphore.h>
#include <time.h>
int main (int argc, char** argv) {
FILE *configFile;
int i,j;
int CashDesksNo=0;
int maxCashDesksNo;
int n,m;
int TmaxServe;
int custPerc; //customer ratio policy
int maxCapacity;
char * nlptr=NULL;
char * pch=NULL;
char line[125];
char termInput[30];
char tmpString[40];
int flg1,flg2;
int flag;
int execResult=0;
int fd;
int rc;
int randNum;
int status;
pid_t ch_pid;
int a,b,c;
int shmid=0;
int *shm_ptr;
int * err;
int retval;
sem_t *sp;
char semName[10];
strcpy(semName,"mutex");
//---------- Davasma kai elegxos in line parameters-----------------
// read inline params and config file
.
.
.
//------------ Print Configuration Data ----------------------------
if(CashDesksNo>maxCashDesksNo || CashDesksNo<1)
{
printf("n# of Cash Desks should be between 1 and %d",maxCashDesksNo);
printf("nsupermarket will now exit...n");
exit(1);
}
printf("n//-----------------------------------------------");
printf("nSupermarket initialization");
printf("n# of Cash Desks: %d",CashDesksNo);
printf("n# of max products: %d",n);
printf("nMax price: %d",m);
printf("nMaximum serving time(secs): %d",TmaxServe);
printf("n%% Customer/Cashier Percentage: %d/%d",custPerc,100-custPerc);
printf("nMax Supermarket capacity: %d",maxCapacity);
printf("n//-----------------------------------------------n");
printf("nAbout to create customer and cashier processes");
// ----------- Shared Memory Attachment --------------------------------
shmid=shmget(IPC_PRIVATE,sizeof(int*),0666);
if (shmid < 0)
{
perror("shmget");
exit(1);
}
shm_ptr=(int*)shmat(shmid,(void *)0,0);
if (shm_ptr == (int *)(-1))
{
perror("shmat");
exit(1);
}
a=0; //shm
shm_ptr=(int*)a;
printf("shmPtr:%d",(int)shm_ptr);
// ----- create & initialize semaphore ---------------------------------
sp = sem_open(semName,O_CREAT,0644,1);
if(sp == SEM_FAILED)
{
perror("unable to create semaphore");
exit(-1);
}
while(1)
{
printf("nPress enter to start a new day at the supermarket(type exit to quit)n");
fgets(termInput,sizeof(termInput),stdin);
nlptr = strchr(termInput, 'n');// termatismos string
if (nlptr) *nlptr = ' ';
if(strcmp(termInput,"exit")==0)//exit apo tin efarmogi
{
printf("nExiting Supermarket..n");
exit(0);
}
i=0;
while(i<maxCapacity)
{
//-Fork new process for the simulation --------------------
ch_pid = fork();
if (ch_pid == -1) {
perror("nFailed to fork initial spliter/merger process n");
exit(1);
}
if ( ch_pid == 0 ) //this is the child process
{
srand (getpid());//pid based seed
// "itoa" - Metatropi ari8mou se string
sprintf( tmpString, "%d", shmid );
randNum=rand() % 100 + 1;
if(randNum<custPerc)// customer : cashier ratio
{
execResult=execl("customer","customer","0",tmpString,NULL);
//printf("nCreated a customer,randNum %d",randNum);
}else
{
execResult=execl("cashier","cashier","0",tmpString,NULL);
//printf("nCreated a cashier,randNum %d",randNum);
}
if(execResult==-1)
{
perror("Could not perform exec to create cashier/customer process");
}
}
i++;
}
//Root process
//wait for childs to terminate
for (i = 0; i < maxCapacity; ++i)
{
waitpid(-1,&status,0);
}
printf("supermarket shared memory content: %d",(int)shm_ptr);
sem_close(sp);
sem_unlink(semName);
err = (int*)shmctl(shmid, IPC_RMID, 0);
if (err == -1)
perror ("Shared Memory Removal.");
else
printf("Shared Memory Removed. %dn", (int)(err));
}
}
这是生成文件：
OBJS = supermarket.o cashier.o customer.o
SOURCE = supermarket.c cashier.c customer.c
HEADER = struct.h
OUT = supermarket cashier customer
CC = gcc
FLAGS = -lrt -g -c
LIBS = -lm
# -g option enables debugging mode
# -c flag generates object code for separate files
# -lm math library
all: supermarket cashier customer
supermarket: supermarket.c
$(CC) supermarket.c -o supermarket
cashier: cashier.c
$(CC) cashier.c -o cashier
customer: customer.c
$(CC) customer.c -o customer
# clean house
clean:
rm -f $(OBJS) $(OUT)
# do a bit of accounting
count:
wc $(SOURCE) $(HEADER)
我一直收到这个错误：
george@george-System-Product-Name:~/Desktop/prj3$ make
gcc supermarket.c -o supermarket
supermarket.c: In function ‘main’:
supermarket.c:310:11: warning: comparison between pointer and integer [enabled by default]
/tmp/ccYxA2Wi.o: In function `main':
supermarket.c:(.text+0x75c): undefined reference to `sem_open'
supermarket.c:(.text+0x9b0): undefined reference to `sem_close'
supermarket.c:(.text+0x9bf): undefined reference to `sem_unlink'
collect2: ld returned 1 exit status
make: *** [supermarket] Error 1
我能做什么？这是一个操作系统类的项目，我的系统是linux Ubuntu
我认为你也应该链接到pthread：
-lpthread
示例makefile来自我的一个旧项目（见评论）：
CC=gcc
CFLAGS=-c -Wall -O3 -g
LDFLAGS=-pthread
SOURCES=chatzor.c clientlist.c messagequeue.c
OBJECTS=$(SOURCES:.cpp=.o)
EXECUTABLE=chatzor_server
all: $(SOURCES) $(EXECUTABLE)
$(EXECUTABLE): $(OBJECTS)
$(CC) $(LDFLAGS) $(OBJECTS) -o $@
.cpp.o:
$(CC) $(CFLAGS) $< -o $@
clean:
rm -rf *.o ${EXECUTABLE}
做完这件事后，你会感到小腿酸痛。
编译跟踪显示：
$ make
gcc supermarket.c -o supermarket
supermarket.c: In function ‘main’:
...
你的makefile上写着：
supermarket: supermarket.c
$(CC) supermarket.c -o supermarket
它应该说（至少）：
supermarket: supermarket.c
$(CC) supermarket.c -o supermarket $(LIBS)
事实上，它可能应该说：
supermarket: supermarket.c
$(CC) $(CFLAGS) supermarket.c -o supermarket $(LDFLAGS) $(LIBS)