Error while getting data from a file

[nickyeng]

Hi

My case is i get the error on runtime while getting data from a file.
i get this error:

Record of 12344 is found!
       5 [main] testing 4272 _cygtls::handle_exceptions: Error while dumping state (probably corrupted stack) 
Segmentation fault (core dumped)
 

I use cygwin gcc package to compiled it.
here is the code that i thought it might the error area:

char line[100];
char *title[] = {"Student ID", "Student Name", "Subject Code", "Mark"}
printf("\nRecord of %s is found!\n", id);
 
while(fgets(line, 100, ptr) != NULL) {   // read line by line
 
    char word[20];
 
        int n;
    int i;
 
    for(n = 0; n < strlen(line); n++)
    {
        if( line[n] == ' ' )   // See if it is a space
        {
            strncpy(word, line, n);   
            line = strstr(line, " ");     // get the whole line from first occurrances of " ".
            printf("%s : %s\n", title[i++], word);
        }
    }
    line = "";    // set the line to blank
    break;
}
 

anyone helps?

[horace1]

try printing the records as you read them with fgets() - you will then be able to see which record caused the segmentation error. I would assume you have exceeded an array bounds. For example, could this copy > 20 characters?

            strncpy(word, line, n);   
 

or could i be greater than 3?

            printf("%s : %s\n", title[i++], word);
 

[nickyeng]

the data from file is the format like this:
------------------------------------
data1 data2 data3 data4
......
------------------------------------

each data wont exceed > 20 characters.

so this problem is not an issue.

Next,
the i variable wont be incremented unless the if block runs, right? so i have no idea what else get wrong..

thanks for the info.

[horace1]

just noticed i is not initialised - it is a local variable so its value will be undefined.
you need to

    int i=0;  // ** set i = 0
 

strdncpy() does not null terminate a string if the length of the string in line is > n, you need to make sure it is null terminated, e.g.

            strncpy(word, line, n);  
            word[n]='\0'; 
 

[horace1]

think this is what you need

    int n;
    int i=0;  // ** set i = 0
 
    for(n = 0; n < strlen(line); n++)
    {
        if( line[n] == ' ' )   // See if it is a space
        {
        strncpy(word, line, n);  
                word[n]='\0';                  // null terminate
            line = strstr(line+1, " ");     // get the whole line from first occurrances of " ".
        printf("%s : %s\n", title[i++], word);
        n=0;                             // reset to start of new string
        }
    }
 

what if the Student name has a space in it?

[horace1]

any reason why you don't use sscanf() to extract the data from your input, e.g.

    char *title[] = {"Student ID", "Student Name", "Subject Code", "Mark"};
    char data[100]="data1 data2 data3 data4 ";
    char id[10], name[10], code[10], mark[10];
    sscanf(data, "%s%s%s%s", id, name, code, mark);
    printf( "%s %s\n %s %s\n %s %s\n %s %s\n",
         title[0], id, title[1], name, title[2], code, title[3], mark);
 

when run gives
Student ID data1
Student Name data2
Subject Code data3
Mark data4

[nickyeng]

the reason is i must save data into a file, and any function in the program need data from a file, then i must retrieve data from file.

[horace1]

the reason is i must save data into a file, and any function in the program need data from a file, then i must retrieve data from file.

what about fscanf()
http://www.cplusplus.com/reference/clibrary/cstdio/fscanf.html

e.g. reading one recond

  FILE * pFile;
  char *title[] = {"Student ID", "Student Name", "Subject Code", "Mark"};
  char id[10], name[10], code[10], mark[10];
  pFile = fopen ("myfile.txt","r");
  if(pFile == NULL)
    { printf("file open failed!"); system("pause"); exit(1); }
  fscanf(pFile, "%s%s%s%s", id, name, code, mark);
  printf( " %s %s\n %s %s\n %s %s\n %s %s\n",
         title[0], id, title[1], name, title[2], code, title[3], mark);
  fclose (pFile);
 

[nickyeng]

what if i have these data in a file:
-------------------------------------
data1 data2 data3 data4
dat1 dat2 dat3 dat4
......
...... // keep continue to have data
-------------------------------------

your fscanf is works with one line data i think.

[nickyeng]

it works with feof using while loop.

thanks for the info, horace1