File Input/Output operations

Previous activities

Table of Contents

1. Converting (and copying) a file to uppercase

Resources
Work Plan

2. Working with a file that contains information about students

Resources
Work Plan

1. Converting (and copying) a file to uppercase

Resources

For this activity, you should revise the fwrite and fread functions and toupper
Section 4 from Reading and writing with files .

Work Plan

To read from a file a specific number of bytes, it is useful the fread function: size_t fread(void *restrict ptr, size_t size, size_t nitems, FILE *restrict stream);. This function reads nitems objects, each size bytes long, from the stream pointed to by stream, storing them at the location given by ptr.

The fread function returns the number of objects read. If an error occurs, or the end-of- file is reached, the return value is a short object count (or zero).

As the fread function does not distinguish between end-of-file and error; callers must use feof() and ferror() to determine which occurred.
The feof function: int feof(FILE *stream); tests the end-of-file indicator for the stream pointed to by stream, returning non-zero if it is set.
The inverse function of fread is the fwrite function: size_t fwrite(const void *restrict ptr, size_t size, size_t nitems, FILE *restrict stream);

This function writes nitems objects, each size bytes long, to the stream pointed to by stream, obtaining them from the location given by ptr.

The fwrite function returns the number of objects written. The function fwrite() returns a value less than nitems only if a write error has occurred.
The toupper function converts a char to uppercase int toupper (int c);. The return value is the character c converted to uppercase or c otherwise. This function is included in the library ctype.h.

Write a program with name convert_to_uppercase.c that implements the following operations:
1. Check that the program is executing with two arguments. If that is not the case, print a message and terminate.
2. Open with reading permissions the file using as name the first argument given to the program. If the operation fails, notify with a message and terminate the execution.
3. Open with writing permissions the file using as name the second argument given to the program. If the operation fails, notify with a message and terminate the execution.
4. Reads SIZE bytes of the input file (first argument) using the fread function and transforms each character into uppercase (use a loop, taking care of converting only the number of read bytes)
  
  Writes using fwritethe converted characters.
  
  The program must convert all the file to uppercase.
5. Close the input and output files

2. Working with a file that contains information about students

Resources

Section 4 from Reading and writing with files .

Work Plan

You should know the following concepts:

To read from a file a specific number of bytes, it is useful the fread function: size_t fread(void *restrict ptr, size_t size, size_t nitems, FILE *restrict stream);. This function reads nitems objects, each size bytes long, from the stream pointed to by stream, storing them at the location given by ptr.

The fread function returns the number of objects read. If an error occurs, or the end-of- file is reached, the return value is a short object count (or zero).

As the fread function does not distinguish between end-of-file and error; callers must use feof() and ferror() to determine which occurred.
The feof function: int feof(FILE *stream); tests the end-of-file indicator for the stream pointed to by stream, returning non-zero if it is set.
The inverse function of fread is the fwrite function: size_t fwrite(const void *restrict ptr, size_t size, size_t nitems, FILE *restrict stream);

This function writes nitems objects, each size bytes long, to the stream pointed to by stream, obtaining them from the location given by ptr.

The fwrite function returns the number of objects written. The function fwrite() returns a value less than nitems only if a write error has occurred.
The mkstemp function: int mkstemp(char *template), generates a unique temporary file name from template.

The last six characters of template must be “XXXXXX” and these are replaced with a string that makes the filename unique. The file is then created with mode read/write.

Since it will be modified, template must not be a string constant, but should be declared as a character array.

The mkstemp function returns the file descriptor fd of the temporary file or -1 on error. Notice that the file descriptor is an int.
In order to open a file using its file descriptor, you must use the fdopen function: FILE *fdopen(int fildes, const char *mode)

This function behaves as the fopen function, but instead of opening a file using its path, it uses the file descriptor.
In order to move the file position indicator for a stream, the fseek function must be used: int fseek(FILE*stream,long offset,int whence);.

This function sets the file position indicator for the stream pointed to by stream. The new position, measured in bytes, is obtained by adding offset bytes to the position specified by whence. If whence is set to SEEK_SET, SEEK_CUR, or SEEK_END, the offset is relative to the start of the file, the current position indicator, or end-of-file, respectively.
The rewind function: void rewind(FILE*stream) sets the file position indicator for the stream pointed to by stream to the beginning of the file.
The remove function: int remove(const char *pathname), deletes a name from the file system.
The rename function : int rename(const char *oldpath, const char *newpath), renames a file, moving it between directories if necessary.

Data of the scores of a group of students is stored in a file. This file has the following structure:

Figure 1. File structure

Where id_c is the group identifier (4 bytes); id_s the student identifier (4 bytes); size_n the size of the name of the student, including the zero(4 bytes); name, the name of the student (including the zero);n_scores the number of scores stored for this student (an integer of 4 bytes); score_i, the i score of this student (4 bytes).

If n_scores is equal to zero, the student has no scores.

You are asked to:
1. Definition of the needed data structures to store all this information in a linked list.
2. Code a function that reads from the file and stores all this information in a linked list. This function has as input parameters the list where to store all this information and the filename.
3. Code a function that, given the data of a student (id and name), inserts him/her at the begining of the file. This function must check if the student data are already stored, and if not, it must insert her/him with 0 scores. As input parameters, this function has the student data and the filename. You must use the mkstemp function to create a temporary file.
4. Code a function that, given the data of a student (id and name), deletes him/her (and all his/her data, including scores) from the file. As input parameters, this function has the student data and the filename. You must use the mkstemp function to create a temporary file.

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Telematic/Audiovisual Syst./Communication Syst. Engineering

Systems Architecture

September 2015 - January 2016