Question

I have an assignment that is supposed to be written in C (not C++), in which I need to create some structs from reading multiple text files. I have learnt c before (2 years ago) – I’m far more comfortable with Java, just can’t use that for this project. I guess my issue comes from not understanding the pointer syntax very well :/.
However, my real issue:

The code I have written crashes when I try to use the strcpy function:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

typedef struct{
    char* filename;
    int time;
} JOB;

JOB **jobQueue;
int nJobs;

void trimLine(char* line) {
    for (int i = strlen(line); i >=0; i--) {
        if (line[i] == '\n' || line[i] == '\r') line[i] = '\0';
    }
}

int main(int argc, char* argv[]) {
    if (argc !=2) {
        printf("Error - Usage is: my_project file\n");
        exit(-1);
    }
    FILE *fp;
    fp = fopen(argv[1],"r");
    if (fp==NULL) {
        printf("Error - file %s could not be read.\n",argv[1]);
        exit(-1);
    }
    jobQueue = malloc(3*sizeof(JOB*));
    char filename[BUFSIZ];
    nJobs = 0;
    while (fgets(filename,sizeof(jobfilename),fp)!=NULL) {
        trimLine(filename);    
        JOB* newjob;
        newjob = malloc(sizeof(JOB));
            //** THIS IS WHERE IT SCREWS UP
        strcpy(newjob->filename,filename);

        jobQueue[nJobs++] = newjob;
    }
}

If I delete the line containing strcpy, the program runs fine (well, I realise this part doesn’t really do anything, but still). However, when the program contains the strcpy line, it breaks when attempting to do Job #2. Any idea why?

Also: If I need to maintain an array of JOBs for use in other functions, is the way I have done it correct? JOB **jobQueue is an array of pointers to JOBs, JOB *newjob is a pointer to a JOB, would this work correctly?

Answer 1

newjob->filename is a wild pointer(not set to anything), you have to allocate memory before you can store things at it.