命名管道Linux

Question

I tried run this code, but when I read from pipe, there is no information:

Statitics:
Hora de inicio:(null)
Total pedidos:0
Pedidos recusados:0
Dominios locais:0
Dominios externos:0
Hora atual:17:5:14

I dont't know what is wrong... I need help.

typedef struct{
   int pedidos;
   int loc;
   int ext;
   int rej;
   char* start;
} esta;
int fdpipe;
fd_set write_set;

//PROCESS 1--------------------------------------------------------------

Writer:

esta* estatisticas;

estatisticas=(esta* )malloc(sizeof(esta));
estatisticas->start=convertTime(time(NULL));

 estatisticas->ext=1;
 estatisticas->loc=1;
 estatisticas->rej=1;
estatisticas->pedidos=1;

if (mkfifo(mpconfs->pipe_stats,0600)<0)
{
        perror("Cannot create pipe: ");
        exit(0);
}
//escrever no pipe
if ((fdpipe=open(mpconfs->pipe_stats, O_WRONLY)) < 0)
{
        perror("Cannot open pipe for writing: ");
        exit(0);
}

while(1) {
    //escrever no pipe
    FD_ZERO(&write_set);

    FD_SET(fdpipe, &write_set);



    if (select(fdpipe+1, NULL, &write_set, NULL, NULL)>0) {
        if(FD_ISSET(fdpipe,&write_set)){
            write(fdpipe, &estatisticas, sizeof(esta));
        }
    }
}

---

reader: //PROCESS 2------------------------------------------------------------

fd_set read_set;
esta* estatisticas;
signal(SIGINT,catch_ctrlcProcEsts);

sleep(2);
if ((fdpipe=open(mpconfs->pipe_stats, O_RDWR)) < 0)
{
    perror("Cannot open pipe for reading: ");
    exit(0);
}

while(1){

    FD_ZERO(&read_set);
    // prepares read set to "listen" to the following FD
    FD_SET(fdpipe, &read_set);
    if (select(fdpipe+1, &read_set, NULL, NULL, NULL)>0) {
        if(FD_ISSET(fdpipe,&read_set)){

            read(fdpipe, &estatisticas, sizeof(esta));
            imprimeStats(estatisticas);
        }
    }

}
}

void imprimeStats(esta* estatisticas){
   char *horaAtual=convertTime(time(NULL));
   printf("\nStatitics:\n");
   printf("Hora de inicio:%s\n",estatisticas->start);
   printf("Total pedidos:%d\n",estatisticas->pedidos);
   printf("Pedidos recusados:%d\n",estatisticas->rej);
   printf("Dominios locais:%d\n",estatisticas->loc);
   printf("Dominios externos:%d\n",estatisticas->ext);
   printf("Hora atual:%s\n\n",horaAtual);
}

   char *convertTime(time_t time){
   char *res;
   int h, min, sec;
   res=(char*)malloc(9*sizeof(char));
   res[0]='\0';

   h=(time/3600);
   min=(time-3600*h)/60;
   sec = time%60;
   h=h%24;
   sprintf(res,"%d:%d:%d", h, min, sec);
   return res;
}

I think that I don't forget anything.

Answer 1

you probably misuse the read an write: you write read(fdpipe, &estatisticas, sizeof(esta)); but declared esta* estatisticas; thus you actually send the address you allocate plus some garbage (undefined behaiour)

you probably intended to write: read(fdpipe, estatisticas, sizeof(*estatisticas))

BTW you should check the amount of byte that you read as read done not always read all the byte you asked for (may be less)

Careful, you did the same error on the write side, don't forget to fix it there too.