Question

I am having some problem with writing a function to extract strings from a file as part of a bigger program. Everything seems to be working fine, except when I use memset or bzero to erase the character arrays I have been using. I have been sitting with this problem for more than an hour and I keep getting seg faults whatever I do. I am getting this error for both bzero and memset. Please help me out.
I am attaching my code below. The statement “Come out of addfront” is printed but none of the “Done with all bzero” statements are printing. I get a segmentation fault at that point. Thank you

void extractFileData(FILE *fp , char clientName[])
{
    char tempFileName[50], tempFilePath[100], tempFileSize[50];
    struct stat fileDetails;

    while(fgets(tempFileName, sizeof(tempFileName), fp)!= NULL)
    {
        if((newLinePos = strchr(tempFileName, '\n')) != NULL)
        {
            *newLinePos = '\0';
        }

        strcat(tempFilePath, "SharedFiles/");
        strcat(tempFilePath, tempFileName);

        if(stat(tempFilePath, &fileDetails) < 0)
        {
            perror("Stat error");
            exit(1);
        }

        //Copy it into a string
        sprintf(tempFileSize, "%zu", fileDetails.st_size);
        printf("temp file size: %s\n", tempFileSize);

        //Add all these details to the file list by creating a new node
        addFront(tempFileName, tempFileSize, clientName);

        printf("Come out of addfront\n");

        memset(&tempFileName, 0, 45);
        printf("Done with all bzero\n");
        memset(&tempFileSize, 0, sizeof(tempFileSize));
        memset(&tempFilePath, 0, sizeof(tempFilePath));

        printf("Done with all bzero\n");
    }
}   

EDIT:

void addFront(char fileName[], char fileSize[], char clientName[])
{
    FILENODE* n;
    printf("Inside add front function\n");
    strcpy(n->fileName, fileName);
    printf("n->filename: %s\n", n->fileName);
    strcpy(n->fileSize, fileSize);
    printf("n->filesize: %s\n", n->fileSize);
    strcpy(n->ownerName, clientName);
    printf("n->ownername: %s\n", n->ownerName);
    myFileList.head = n;
    printf("Did it go past myfilelist head = n\n");
    myFileList.numOfNodes++;
    printf("num of nodes: %d\n", myFileList.numOfNodes);
}

I have added my code for the addFront function. It basically adds
the details to a struct myFileList which is basically an implementation
of a linked list. The FILENODE represents each entry in the list.

EDIT:

Adding the structs I am using

 struct fileNode
 {
      char fileName[50];
      char fileSize[50];
          char ownerName[25];
      struct fileNode* next;
 };

 struct fileList
 {
      struct fileNode* head;
      struct fileNode* tail;
       int numOfNodes;
 };

 typedef struct fileList FILELIST;
 typedef struct fileNode FILENODE;

Answer 1

I don’t know why your program would crash there. But I can another error in the program. Fix the other error first, see if you still have problems.

This is wrong:

strcat(tempFilePath, "SharedFiles/");
strcat(tempFilePath, tempFileName);

The tempFilePath variable is uninitialized. This may coincidentally not crash, but you cannot rely on it not to crash. It may scribble on your stack.

Do this instead:

snprintf(tempFilePath, sizeof(tempFilePath), "SharedFiles/%s", tempFileName);

Finally, there is no need to zero the arrays. The contents of the arrays are not used in the next loop iteration, so you might as well ignore them.

void extractFileData(FILE *fp , char clientName[])
{
    char tempFileName[50], tempFilePath[100], *newLinePos;
    struct stat fileDetails;
    while (fgets(tempFileName, sizeof(tempFileName), fp)) {
        if ((newLinePos = strchr(tempFileName, '\n')))
            *newLinePos = '\0';
        snprintf(tempFilePath, sizeof(tempFilePath),
                 "SharedFiles/%s", tempFileName);
        if (stat(tempFilePath, &fileDetails) < 0) {
            perror("Stat error");
            exit(1);
        }
        printf("temp file size: %zu\n", tempFileSize);
        addFront(tempFileName, tempFileSize, clientName);
    }
}   

The snprintf() function is really the number one choice for doing work like this in C. It’s easy to write code with snprintf() that “obviously won’t crash”, as opposed to code that “won’t obviously crash”.

If your code still crashes, there is an error somewhere else.