Thread: Segmentation fault problem

Good day everyone.

I just want to know if I'm doing everything right in 2 of my functions. First off, the function inserttolist just connects the node created by parse_file. The linked list contains parts of a file, which I send to another PC. I didn't put this into the networking section because I think that the networking part of my code is already working.

There are two problems that I encounter when using these functions. First, when I try to allocate a small memory size for my chunksize(say 100bytes), a segmentation fault usually happens.

Another problem that I encounter is when I try to traverse the list, a segmentation fault SOMETIMES happen. If for example, I traversed it in one go(meaning, traverse the first node until the last), it runs fine. But when I traverse it when I need to resend a part of the file which is lost(since this is used in a file transfer program), it sometimes encounter a segmentation fault.

For the linked list:

Code:

struct flist{                //linked list for file chunk       
        char *chunk;            //file segment
        int chunksize;            //size of chunk of this node
        int isn;            //segment number of packet
        int res;
        int last;
        int acked;
        struct flist *next;        //pointer to the next node
    };
    typedef struct flist Flist;    
    Flist *fileparse = NULL;        //define pointer of struct flist

For the parse_file:

Code:

void parse_file(Flist* sPtr, int chunksize, int isn, char filename[]){                
    FILE *ptr;                //file pointer
    char *buffer1, *buffer2;                //pointer to memory holding each chunk
    int quotient;                //counter for f
    int modulo;
    size_t res;                //for fread
    int counter = 0;                //just a counter
    
    /*open file*/
    if ((ptr = fopen(filename, "r+b")) == NULL)            //if file cannot be opened..
    {
        printf("File open error\n");
        goto end;
    }
    else{
    /*obtain file size*/
    fseek (ptr , 0 , SEEK_END);
      filesize = ftell (ptr);
     rewind (ptr);
    }
    /*obtain number of chunks to be made*/
    if(filesize<chunksize){
        printf("File size is too small for chunk\n");
        quotient = 0;
        modulo = filesize;
        goto start;
    }
    quotient = filesize/chunksize;
    modulo = filesize%chunksize;
        printf("Modulo is %i\n",modulo);

    start:
    buffer1 = (char *)malloc(sizeof(char)*chunksize);        //allocate memory for chunk
    buffer2 = (char *)malloc(sizeof(char)*modulo);        //allocate memory for chunk
    /*start getting the chunks*/
    while(1){
        if(counter!=quotient){
            memset(buffer1,0,chunksize);
            if(buffer1 == NULL){
                printf("Allocation failed\n");
                goto end;
            }
            res = fread(buffer1,sizeof(char),chunksize,ptr);    //get the chunk from file pointer
              if (res != chunksize){
                goto end;
            }
            inserttolist(sPtr,res,isn,buffer1,0,res,modulo);
            counter++;                        //increment counter
            isn = isn + res;                            //increment segment number
            
        }
        else if((counter == quotient) && (modulo != 0)){
            memset(buffer2,0,modulo);
            if(buffer2 == NULL){
                printf("Allocation failed\n");
                goto end;
            }
            res = fread (buffer2,sizeof(char),modulo,ptr);    //get the chunk from file pointer
            inserttolist(sPtr,res,isn,buffer2,1, res,modulo);
            break;
        }
    }
    end:
    
    fclose(ptr);
        
}

For the inserttolist:

Code:

void inserttolist(Flist *sPtr, int chunksize, int isn, char *buffer, int last, int res, int modulo){
    while(sPtr->next != NULL){        
            sPtr = sPtr->next;                    //find end of list
                
        }
        sPtr->next = (struct flist *)malloc(sizeof(struct flist));    //allocate memory for node
        sPtr->next-> res = res;
        sPtr->next->chunksize = chunksize;                //size of the chunk pointed by sptr->chunk
        sPtr->next->isn = isn;                        //segment number of this chunk
        sPtr->next->next = NULL;
        sPtr->next->acked = 0;
        if(last == 0){
            sPtr->next->last = 0;
            sPtr->next->chunk = (char *)malloc(sizeof(char)*chunksize);        //set sptr->chunk to point to the actual chunk        
            memcpy(sPtr->next->chunk,buffer,chunksize);
        }
        else{
            sPtr->next->last = 1;
            sPtr->next->chunk = (char *)malloc(sizeof(char)*modulo);        //set sptr->chunk to point to the actual chunk
            memcpy(sPtr->next->chunk,buffer,modulo);
        }


}

Thank you for taking the time in reading this and I hope you can help