Saving struct to a file in C - c

Question

In my assignment I was given two functions to write
int openFileFromConsole(FILE *fp)
It takes an empty file pointer as input to the function using call by reference. And updates the pointer to point to the appropriate HDD address. IMPORTANT: Later, it asks the user through the console to provide the name and also asks for the file open type: "w", "r", "a" and UPDATES the file pointer. It returns 1 if succeeded, or 0 if fails.
void saveStudentGradeInfoTofile(FILE *fp)
This function gets the student info and saves it first into the student data-type (which is struct but disguised using typedef) then saves it to file. The student information is being provided by the register through the console. This takes the file pointer by reference as input and update the file using fprint.
This program is supposed to open a file through console depending on the user input then collect information and store them to a struct and save it to that file.I have written the two functions(correctly I think?).But I am having a hard time implementing them to main() since the first one is an int type function.Any help would be appreciated.
typedef struct student {
char name[50];
char id [20];
int score;
}student;
int openFileFromConsole(FILE *fp);
void saveStudentGradeInfoTofile(FILE *fp);
int main()
{
return 0;
}
int openFileFromConsole(FILE *fp){
char filePath[100],fileOpenType[10];
printf("Enter Path name: ");
scanf("%s", filePath);
printf("Enter file open type w, r or a: ");
scanf("%s", fileOpenType);
fp = fopen(filePath,fileOpenType);
if(fp != NULL) {
printf("File has been opened");
return 1;
}
else printf("File not found");
return 0;
}
void saveStudentGradeInfoTofile(FILE *fp){
int numOfStudent ;
student s[100];
printf ("Get the number of students :");
scanf("%d",&numOfStudent);
for(int i = 0; i < numOfStudent; i++) {
printf("\nEnter ID number:");
scanf(" %s",s[i].id);
printf("Enter name: ");
scanf("%s,",s[i].name);
printf("Enter score: ");
scanf("%d",&s[i].score);
fprintf(fp,"id : %s, Name: %s, score =%d\n",s[i].id,s[i].name,s[i].score);
printf("\n");
}
}

Answer 1

the posted code has a few problems.
it does not follow the axiom: only one statement per line and (at most) one variable declaration per statement. The result is the code is much more difficult to understand, debug, maintain.
The calls to system functions need to have their returned values checked to assure the operation was successful.
To modify where a pointer, located in the calling function, points, the pointer must be passed as a 'pointer to a pointer'.
when calling any of the scanf() family of functions, when using the '%s' input conversion specifier, always include a MAX CHARACTERS modifier that is 1 less than the length of the input buffer, so the user cannot overrun the input buffer. Such overrun results in undefined behavior and can lead to a seg fault event.
when using the '%s' input conversion specifier, insert a space before the specifier to consume any leading 'white space', like any newline sequence.
always cleanup when exiting a program. Do not leave the cleanup to the OS.
when working with numeric values that will never be less than 0, it is best to use size_t rather than int
The posted code is never reading from the student grade info file, so should never be opened with r
the 'mode' in a call to fopen() is always a string, even if it is only a single char, so needs to be written as "w" not just a w
the code contains lots of 'magic' numbers. 'magic' numbers are numbers with no basis. Such numbers make understanding, debugging, etc much more difficult than necessary. Suggest using an enum statement or #define statements to give those 'magic' numbers meaningful names, then use those meaningful names throughout the code.
for ease of readability and understanding, consistently indent the code. indent after every opening brace '{'. unindent after every closing brace '}'. Suggest using 4 spaces for each indent level as that is visible even with variable width fonts.
it is a poor programming practice to combine a 'struct' definition with a 'typedef'. code them separately.
when posting code, include the needed header file statements, so we do not have to guess what your code actually uses.
for ease of readability and understanding, separate code blocks (for, if, else, while, do...while, switch, case, default) via a single blank line. Separate functions by 2 or 3 blank lines (be consistent).
While modern compilers will handle the duplication of names, as modern compilers keep the struct names in a separate namespace from the typedef names, it is a poor programming practice that easily leads to confusion. Suggest keeping names unique (although that was not followed in this answer.
Here is a possible implementation of the desired functionality:
#include <stdio.h> // fopen(), fclose(), perror(), FILE
#include <stdlib.h> // exit(), EXIT_FAILURE
enum {
MAX_NAME_LEN =50,
MAX_ID_LEN =20,
MAX_PATH_LEN =100,
MAX_TYPE_LEN =10,
MAX_NUM_STUDENTS =100
};
struct student
{
char name[ MAX_NAME_LEN ];
char id [ MAX_ID_LEN ];
int score;
};
typedef struct student student;
int openFileFromConsole(FILE **fp);
void saveStudentGradeInfoTofile(FILE *fp);
int main( void )
{
FILE * fp = NULL;
int openStatus = openFileFromConsole(&fp);
if( 0 == openStatus )
{
saveStudentGradeInfoTofile( fp );
}
fclose( fp );
return 0;
} // end function: main
int openFileFromConsole(FILE **fp)
{
char filePath[ MAX_PATH_LEN ];
char fileOpenType;
printf("Enter Path name: ");
if( 1 != scanf("%100s", filePath) )
{
perror( "scanf for file path failed" );
exit( EXIT_FAILURE );
}
// implied else, scanf successful
printf("Enter file open type w, r or a: ");
if( 1 != scanf(" %c", &fileOpenType) )
{
perror( "scanf for file open type failed" );
exit( EXIT_FAILURE );
}
// implied else, scanf successful
char buffer[ MAX_TYPE_LEN ];
buffer[0] = '\"';
buffer[1] = fileOpenType;
buffer[2] = '\"';
buffer[3] = '\0';
*fp = fopen(filePath, buffer);
if( *fp )
{
return 1;
}
else
{
perror( "fopen failed" );
return 0;
}
} // end function: openFileFromConsole
void saveStudentGradeInfoTofile(FILE *fp)
{
size_t numOfStudent;
student s[ MAX_NUM_STUDENTS ];
printf ("Get the number of students :");
if( 1 != scanf("%lu",&numOfStudent) )
{
perror( "scanf for number of students failed:" );
fclose( fp );
exit( EXIT_FAILURE );
}
// implied else, scanf successful
for( size_t i = 0; i < numOfStudent; i++)
{
printf("\nEnter ID number:");
if( 1 != scanf(" %19s",s[i].id) )
{
perror( "scanf for student ID failed" );
fclose( fp );
exit( EXIT_FAILURE );
}
// implied else, scanf successful
printf("Enter name: ");
if( 1 != scanf(" %49s,",s[i].name) )
{
perror( "scanf for student ID failed" );
fclose( fp );
exit( EXIT_FAILURE );
}
// implied else, scanf successful
printf("Enter score: ");
if( 1 != scanf("%d",&s[i].score) )
{
perror( "scanf for student Score failed" );
fclose( fp );
exit( EXIT_FAILURE );
}
// implied else, scanf successful
fprintf(fp,"id : %s, Name: %s, score =%d\n",
s[i].id,
s[i].name,
s[i].score);
printf("\n");
} // end while
} // end function: saveStudentGradeInfoToFile

Answer 2

Just in case you want to pass the file path as an argument to your program
int main(int c /* argument counter */, char *v[] /*argument list */)
{
FILE *fp;
if(c >= 2) {
char *path = v[1]; /* this is the second argument (the first one, v[0], is the program's name): ./foo myfile.txt */
fp = fopen(path, "your mode goes here");
/* ... */
}
}