I have a problem with acccessing a char ** in one of my struct.

    uint64_t id;
    struct timing timing;
    //command *command;
    uint32_t argc;
    char ** argv;
} taskR; 

i stock everything in my struct correctly but when it comes to reading it from a file i cant access the argv part whitout a "core dumped " alert (the other arguments work perfectly fine)

        taskR stp;
        uint64_t ip=stp.id;
        read(i,&stp,sizeof(struct task));
        struct timing ti;
        ti=stp.timing;//all good
        printf("%s",stp.argv[0]);//core dumped  

Happy new year everyone :) ty for the answer !!

CodePudding user response：

It will never work. You read only the value of the pointer argv but not the referenced array of pointers and strings assigned to it. Even if you read it they will reference other memory areas than the original ones when written.

You will need to serialize it and save all the underlying data. Then you will need to read it and reconstruct the structure.

example:

typedef struct
{
    unsigned id;
    unsigned timing;
    //command *command;
    unsigned argc;
    char ** argv;
} taskR; 

char *removeLastLF(char *str)
{
    char *wrk = str;
    if(str && str)
    {
        while(*(str   1)) str  ;
        if(*str == '\n') *str = 0;
    }
    return wrk;
}

int mywrite(FILE *fo, taskR *t)
{
    fprintf(fo, "%u,%u,%u\n", t -> id, t -> timing, t -> argc);
    for(unsigned i = 0; i < t -> argc; i   )
    {
        fprintf(fo, "%s\n", t -> argv[i]);
    }
    return 0;
}

taskR *myread(FILE *fi)
{
    char buff[128];
    taskR *t = malloc(sizeof(*t));

    if(t)
    {
        fgets(buff, 128, fi);
        if(sscanf(buff, "%u,%u,%u\n", &t -> id, &t -> timing, &t -> argc) == 3)
        {
            t -> argv = malloc(t -> argc * sizeof(*t -> argv));
            for(unsigned i = 0; i < t -> argc; i   )
            {
                fgets(buff, 128, fi);
                removeLastLF(buff);
                t -> argv[i] = malloc(sizeof(**t -> argv) * strlen(buff)   1);
                strcpy(t -> argv[i], buff);
            }
        }
    }
    return t;
}

It requires much more error checking but I have skipped it for the sake of simplicity.