变量值测试的分段错误

Question

I don't understand why there is a segfault on : while (((*buf)!= ' ')) I would to store a content of a an array in N others array's (N number of thread), but when I store the content of buff I won't to cut a word. I don't understand why there is a segmentation fault when I test the value of *buf??

#include <stdio.h>
#include <pthread.h>
#include <unistd.h>
#include <stdlib.h>
#include <fcntl.h>

#include <ctype.h>

#include <sys/types.h>
#include <sys/stat.h>
#include <sys/mman.h>

#define MAX_WORD_LENGHT 10

void *count_func(void *arg)
{

}
    int main (int argc, char **argv){

        pthread_t *tids;
        char * buf, * save;
        ssize_t cpt;
        int i, j, fd, count, size, decoup;

        if (argc <2 )
        {   
            printf("\n usage : %s [nom_du_fichier] \n ", argv[0]);
            exit(1);
        }

        fd = open(argv[1],O_RDONLY);

         //taille du fichier
        size = lseek (fd,0,SEEK_END);
        printf("\ntaille du fichier : %d octets\n",size);
        lseek(fd,0,SEEK_SET); // repositionement du pointeur au début du fichier.

        count = sysconf(_SC_NPROCESSORS_ONLN);
        count = (count < 1) ? 1 : count;
        char *tabs[count];

        buf =(char *)malloc(size);
        while ((cpt=read(fd,buf, size)) > 0){
            printf("lect en cours \n");
        }
        save=buf;
        while((*buf)!= '\0'){
        printf("carc: %c \n", *buf);
        buf++;
        }

        // répartion des données de buf sur N sous tableau: N correspandant aux nbr
        // de threads
        for (i=0; i< count; i++){
            tabs[i]= (char *) malloc ((size/count)+ MAX_WORD_LENGHT);
        }  
       buf= save; // on sauvgarde l'adresse du début du tableau.
        for (i=0; i<count; i++){
            for (j=0; j<=(size/count); j++, (*buf)!= '\0'){
                    if (j != (size/count)){
                       printf("j:%d \t", j);tabs[i][j] = *buf;        
                       buf++;
                    }else {
                    if (isspace(*buf)){
                        printf("cond 1\n");
                        break;
                    }else{
                       while (((*buf)!= ' ')){ tabs[i][j]= *buf; buf++; j++;}
                        printf("cont: %c \t ", *buf);
                        printf("cond 2\n");
                        break; 
                        }
                    }
                }
            }


        for (i=0; i< count; i++){
            for (j=0; j< (size/count)+1; j++){
            printf("value of tabs[%d][%d] is : %c \n", i, j, tabs[i][j]);
            }
        printf("tabs: %d done \n", i);
        }

        decoup = (size-1)/count;
        tids = (pthread_t *)malloc (sizeof(pthread_t) * count);

        if(tids == NULL)
        {
            printf("main: failed to allocate tids \n");
            exit(-1);
        }
        close(fd);
        buf=save;
        free(buf);
       // free(tabs[0]); free(tabs[1]);free(tabs[2]);free(tabs[3]);
       // free(tids);
        return 0;
    }

    // vim: filetype=cpp:expandtab:shiftwidth=4:tabstop=4:softtabstop=4

Answer 1

This will go beyond the null terminating character of buf unless it finds a space character before.

while (((*buf) != ' '))

Modify to this

while (*buf && *buf != ' ')

If there is no null-terminating char in the buf or if there is but you want to read beyond that then check that you didn't go beyond the size of the buffer. Eg

while (j < size && *buf != ' ')

Also, lseek is not an efficient way to get the size of a file to allocate memory, as you have to go from the start of the file to the end and back to the start again to be able to read. Have a look at fstat .