Can someone please help me with reading strings in structures please?

**daynorb** · 11-27-2011

Hey there,
In this component of a program I'm working on, the first four commands in my else statement are sticking together without letting me input the information I'm asking for. I had the same problem yesterday, but only the first two were sticking together. Then suddenly I open it this morning and now FOUR are stuck.
Any suggestions would be Fantastic thanks!
Cheers

Code:

char AddStudent()
{
    FILE *fptr;


    struct Students
    {
        char FirstName[SIZE];
        char LastName[SIZE];
        char StudentNumber[8];
        char Assignments[5][4];
        char Labs[5][4];
        char Midterm[4];
        char Final[4];
    };


    struct Students GNG1106[200];


    fptr=fopen("E://StudentFile.txt", "a+");


    if (fptr == NULL)
        printf("Unable to open file");


    else
    {
        printf("File was opened\n");


        printf("Please enter the first name of the student: ");
        fgets(GNG1106[0].FirstName, SIZE, fptr);


        printf("\nPlease enter the last name of the student: ");
        fgets(GNG1106[0].LastName, SIZE, fptr);


        printf("\nPlease the student's student number: ");
        fgets(GNG1106[0].StudentNumber, 8, stdin);


        printf("\nPlease enter the grade out of 100 for the first assignment: ");
        fgets(GNG1106[0].Assignments[0], 4, stdin);


        printf("\nPlease enter the grade out of 100 for the second assignment: ");
        fgets(GNG1106[0].Assignments[1], 4, stdin);


        printf("\nPlease enter the grade out of 100 for the third assignment: ");
        fgets(GNG1106[0].Assignments[2], 4, stdin);


        printf("\nPlease enter the grade out of 100 for the fourth assignment: ");
        fgets(GNG1106[0].Assignments[3], 4, stdin);


        printf("\nPlease enter the grade out of 100 for the fifth assignment: ");
        fgets(GNG1106[0].Assignments[4], 4, stdin);


        printf("\nPlease enter the grade out of 100 for the first lab: ");
        fgets(GNG1106[0].Labs[0], 4, stdin);


        printf("\nPlease enter the grade out of 100 for the second lab: ");
        fgets(GNG1106[0].Labs[1], 4, stdin);


        printf("\nPlease enter the grade out of 100 for the the third lab: ");
        fgets(GNG1106[0].Labs[2], 4, stdin);


        printf("\nPlease enter the grade out of 100 for the fourth lab: ");
        fgets(GNG1106[0].Labs[3], 4, stdin);


        printf("\nPlease enter the grade out of 100 for the fifth lab: ");
        fgets(GNG1106[0].Labs[4], 4, stdin);


        printf("\nPlease enter the grade out of 100 for the midterm exam: ");
        fgets(GNG1106[0].Midterm, 4, stdin);


        printf("\nPlease enter the grade out of 100 for the final exam: ");
        fgets(GNG1106[0].Final, 4, stdin);




        fprintf(fptr, "%s %s %s %s %s %s %s %s %s %s %s %s %s %s %s", GNG1106[0].FirstName, GNG1106[0].LastName, GNG1106[0].StudentNumber, GNG1106[0].Assignments[0], GNG1106[0].Assignments[1], GNG1106[0].Assignments[2], GNG1106[0].Assignments[3], GNG1106[0].Assignments[4],
                GNG1106[0].Labs[0], GNG1106[0].Labs[1], GNG1106[0].Labs[2], GNG1106[0].Labs[3], GNG1106[0].Labs[4], GNG1106[0].Midterm, GNG1106[0].Final);


    }


    fclose(fptr);
}

**daynorb** · 11-27-2011

sorry, quick-fix. In lines 34 and 38 I changed fptr to stdin. However, those first two commands are still sticking together and not allowing me to input the First Name.
Any suggestions?

**Salem** · 11-27-2011

So what do you actually type in (for example).

> char Final[4];
...
> fgets(GNG1106[0].Final, 4, stdin);
Bear in mind that fgets() will also try to store a \n as well.
So if you type in "100\n", it will try and store "100\n\0" in 4 characters (in other words, no).

You'll get "100\0" alright, but the \n will be left for the next fgets() to deal with (which it will - without reading anything else).

Do this for each step

Code:

char buff[BUFSIZ]
fgets( buff, BUFSIZ, stdin );
// strip the newline (if you want to - see the FAQ for how to do it)
// validate and assign.

For example, validation is making sure no more than 3 characters are typed in, representing an integer in the range 0 to 100.
So you would reject input like "123455566" or "barney rubble" or any other nonsense.

**daynorb** · 11-27-2011

Thanks! I'll give this a try

**daynorb** · 11-27-2011

Unfortunately this didn't really solve the problem.
The main issue is that line

Code:

printf("Please enter the first name of the student: ");
fgets(GNG1106[0].FirstName, SIZE, stdin);

doesn't seem to be happening at all. It skips straight to the next command. I don't understand this problem because it is written just like all my other fgets commands.

Code:

char AddStudent()
{
    FILE *fptr;


    struct Students
    {
        char FirstName[SIZE];
        char LastName[SIZE];
        char StudentNumber[8];
        char Assignments[5][4];
        char Labs[5][4];
        char Midterm[4];
        char Final[4];
    };


    struct Students GNG1106[200];


    fptr=fopen("E://StudentFile.txt", "a+");


    if (fptr == NULL)
        printf("Unable to open file");


    else
    {
        printf("File was opened\n");


        printf("Please enter the first name of the student: ");
        fgets(GNG1106[0].FirstName, SIZE, stdin);


        printf("\nPlease enter the last name of the student: ");
        fgets(GNG1106[0].LastName, SIZE, stdin);


        printf("\nPlease the student's student number: ");
        fgets(GNG1106[0].StudentNumber, 8, stdin);
       }
}

Do you see what I mean?

**Salem** · 11-27-2011

You're still trying to read directly from the file (or stdin) into where you want to store the data, WITHOUT first going through any kind of validation.

If there is more data than you expect - even a single character, then your code is broken.

**daynorb** · 11-28-2011

Do you mean something like this?

Code:

char AddStudent()
{
    FILE *fptr;


    struct Students
    {
        char FirstName[SIZE];
        char LastName[SIZE];
        char StudentNumber[8];
        char Assignments[5][4];
        char Labs[5][4];
        char Midterm[4];
        char Final[4];
    };


    struct Students GNG1106[200];


    fptr=fopen("E://StudentFile.txt", "a");


    if (fptr == NULL)
        printf("Unable to open file");


    else
    {
        printf("File was opened\n");


        fputs("\nPlease enter the first name of the student: ", stdout);
        fflush(stdout);
        if (fgets(GNG1106[0].FirstName, 30, stdin) != NULL)
        {
            char *newline = strchr(GNG1106[0].FirstName, '\n');
            if ( newline != NULL )
            {
                *newline = '\0';
                printf("\nNewline removed");
            }
        }


        fputs("\nPlease enter the last name of the student: ", stdout);
        fflush(stdout);
        if (fgets(GNG1106[0].LastName, 30, stdin) != NULL)
        {
            char *newline = strchr(GNG1106[0].LastName, '\n');
            if ( newline != NULL )
            {
                *newline = '\0';
                printf("\nNewline removed");
            }
        }
}

This straightened things up in my file, but I still have the issue of not having the opportunity to input a value for the First Name

**Adak** · 11-28-2011

My guess is that you have a newline char, already in your input stream. So when you come to the first fgets(), (which takes any input UP TO THE FIRST NEWLINE CHAR), it receives the newline and says "OK, I'm outta here!".

Add a getchar() before the first fgets(), and see if that doesn't stop this nonsense.

**Salem** · 11-28-2011

Well it still has the same problem as it's always had - you're reading directly into where you want the answer to be.

The problem is when your answer exactly fills the buffer and the \n spills over to screw up the next fgets call.

Something like this.

Code:

int readMyString ( char *answer, size_t answersize, FILE *fp ) {
  char buff[BUFSIZ];
  if ( fgets( buff, BUFSIZ, fp ) != NULL ) {
    char *newline = strchr(buff, '\n');
    if ( newline != NULL ) {
      *newline = '\0';
    }
    if ( strlen(buff) >= answersize ) {
      printf("Input too long - max expected=%u\n", answersize );
    } else {
      strcpy(answer,buff);
      return 1; // success
    }
  } else {
    return -1; // file error/eof
  }

  return 0; // failure
}

Which you would call in main with something like

Code:

        fputs("\nPlease enter the first name of the student: ", stdout);
        fflush(stdout);
        readMyString(GNG1106[0].FirstName, sizeof(GNG1106[0].FirstName), stdin);
        fputs("\nPlease enter the last name of the student: ", stdout);
        fflush(stdout);
        readMyString(GNG1106[0].LastName, sizeof(GNG1106[0].LastName), stdin);

You can even make use of the return result to try again, continue with the next question, or give up.

**dmh2000** · 11-28-2011

or
fgets(with a buffer bigger than the expected input)
strtok to get the first token
sscanf to get its value
error if any of these fail

**daynorb** · 11-28-2011

Great thanks to all of you, it's working quite nicely now!

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