#include
#include
#include
#include
#include
const int MAXLEN = 30; /* Size of name buffer */
const char *dirpath = "C:\\temp\\"; /* Directory path for file */
const char *file = "mydata.bin"; /* File name */
/* Structure encapsulating a name and age */
struct Record
{
char name[MAXLEN];
int age;
};
void listfile(char *filename); /* List the file contents */
void updatefile(char *filename); /* Update the file contents */
struct Record *getrecord(struct Record *precord); /* Read a record from stdin */
void getname(char *pname); /* Read a name from stdin */
void writefile(char *filename, char *mode); /* Write records to a file */
void writerecord(struct Record *precord, FILE *pFile);
struct Record * readrecord(struct Record *precord, FILE *pFile);
int findrecord(struct Record *precord, FILE *pFile);
void duplicatefile(struct Record *pnewrecord,
int index, char *filename, FILE *pFile);
int main(void)
{
char filename[strlen(dirpath)+strlen(file)+1]; /* Stores file path */
strcpy(filename, dirpath); /* Copy directory path */
strcat(filename, file); /* and append file name */
/* Choose activity option */
char answer = 'q';
while(true)
{
printf("\nChoose from the following options:"
"\nTo list the file contents enter L"
"\nTo create a new file enter C"
"\nTo add new records enter A"
"\nTo update existing records enter U"
"\nTo delete the file enter D"
"\nTo end the program enter Q\n : ");
scanf("\n%c", &answer);
switch(tolower(answer))
{
case 'l': /* List file contents */
listfile(filename);
break;
case 'c': /* Create new file */
writefile(filename,"wb+");
printf("\nFile creation complete.");
break;
case 'a': /* Append records */
writefile(filename, "ab+");
printf("\nFile append complete.");
break;
case 'u': /* Update existing records */
updatefile(filename);
break;
case 'd':
printf("Are you sure you want to delete %s (y or n)? ", filename);
scanf("\n%c", &answer);
if(tolower(answer) == 'y')
remove(filename);
break;
case 'q': /* Quit the program */
printf("\nEnding the program.", filename);
return 0;
default:
printf("Invalid selection. Try again.");
break;
}
}
return 0;
}
/* Read the name and age for a record from the keyboard */
struct Record *getrecord(struct Record *precord)
{
/* Verify the argument is good */
if(!precord)
{
printf("No Record object to store input.");
return NULL;
}
printf("\nEnter a name less than %d characters:", MAXLEN);
getname(precord->name); /* readf the name */
printf("Enter the age of %s: ", precord->name);
scanf(" %d", &precord->age); /* Read the age */
return precord;
}
/* Read a name from the keyboard */
void getname(char *pname)
{
fflush(stdin);
fgets(pname, MAXLEN, stdin); /* Read the name */
int len = strlen(pname);
if(pname[len-1] == '\n') /* if there's a newline */
pname[len-1] = '\0'; /* overwrite it */
}
/* Write a new record to the file at the current position */
void writerecord(struct Record *precord, FILE *pFile)
{
/* Verify the arguments are good */
if(!precord)
{
printf("No Record object to write to the file.");
return;
}
if(!pFile)
{
printf("No stream pointer for the output file.");
return;
}
/* Write the name & age to file */
size_t length = strlen(precord->name); /* Get name length */
fwrite(&length, sizeof(length), 1, pFile); /* Write name length */
fwrite(precord->name, sizeof(char), length, pFile); /* then the name */
fwrite(&precord->age, sizeof(precord->age), 1, pFile); /* then the age */
}
/* Reads a record from the file at the current position */
struct Record * readrecord(struct Record *precord, FILE *pFile)
{
/* Verify the arguments are good */
if(!precord)
{
printf("No Record object to store data from the file.");
return NULL;
}
if(!pFile)
{
printf("No stream pointer for the input file.");
return NULL;
}
size_t length = 0; /* Name length */
fread(&length, sizeof(length), 1, pFile); /* Read the length */
if(feof(pFile)) /* If it's end file */
return NULL; /* return NULL */
/* Verify the name can be accommodated */
if(length+1>MAXLEN)
{
fprintf(stderr, "\nName too long. Ending program.");
exit(1);
}
fread(precord->name, sizeof(char), length, pFile); /* Read the name */
precord->name[length] = '\0'; /* Append terminator */
fread(&precord->age, sizeof(precord->age), 1, pFile); /* Read the age */
return precord;
}
/* Write to a file */
void writefile(char *filename, char *mode)
{
char answer = 'y';
FILE *pFile = fopen(filename, mode); /* Open the file */
if(pFile == NULL) /* Verify file is open */
{
fprintf(stderr, "\n File open failed.");
exit(1);
}
do
{
struct Record record; /* Stores a record name & age */
writerecord(getrecord(&record), pFile); /* Get record & write the file */
printf("Do you want to enter another(y or n)? " );
scanf("\n%c", &answer);
fflush(stdin); /* Remove whitespace */
} while(tolower(answer) == 'y');
fclose(pFile); /* Close the file */
}
/* List the contents of the binary file */
void listfile(char *filename)
{
/* Create the format string for names up to MAXLEN long */
/* format array length allows up to 5 digits for MAXLEN */
char format[15]; /* Format string */
sprintf(format, "\n%%-%ds Age:%%4d", MAXLEN);
FILE *pFile = fopen(filename, "rb"); /* Open file to read */
if(pFile == NULL) /* Check file is open */
{
printf("Unable to open %s. Verify it exists.\n", filename);
return;
}
struct Record record; /* Stores a record */
printf("\nThe contents of %s are:", filename);
while(readrecord(&record, pFile) != NULL) /* As long as we have records */
printf(format, record.name, record.age); /* Output the record */
printf("\n"); /* Move to next line */
fclose(pFile); /* Close the file */
}
/* Modify existing records in the file */
void updatefile(char *filename)
{ char answer = 'y';
FILE *pFile = fopen(filename, "rb+"); /* Open the file for update */
if(pFile == NULL) /* Check file is open */
{
fprintf(stderr, "\n File open for updating records failed.");
return;
}
struct Record record; /* Stores a record */
int index = findrecord(&record, pFile); /* Find the record for a name */
if(index<0) /* If the record isn't there */
{
printf("\nRecord not found."); /* ouput a message */
return; /* and we are done. */
}
printf("\n%s is aged %d,", record.name, record.age);
struct Record newrecord; /* Stores replacement record */
printf("\nYou can now enter the new name and age for %s.", record.name);
getrecord(&newrecord); /* Get the new record */
/* Check if we can update in place */
if((strlen(record.name) == strlen(newrecord.name)))
{ /* Name lengths are the same so we can */
/* Move to start of old record */
fseek(pFile,
-(long)(sizeof(size_t)+strlen(record.name)+sizeof(record.age)),
SEEK_CUR);
writerecord(&newrecord, pFile); /* Write the new record */
fflush(pFile); /* Force the write */
}
else
duplicatefile(&newrecord, index, filename, pFile);
printf("File update complete.\n");
}
/* Duplicate the existing file replacing the record to be update */
/* The record to be replaced is index records from the start */
void duplicatefile(struct Record *pnewrecord, int index, char *filename, FILE *pFile)
{
/* Create and open a new file */
char tempname[L_tmpnam];
if(tmpnam(tempname) == NULL)
{
printf("\nTemporary file name creation failed.");
return;
}
char tempfile[strlen(dirpath)+strlen(tempname)+1];
strcpy(tempfile, dirpath); /* Copy original file path */
strcat(tempfile, tempname); /* Append temporary name */
FILE *ptempfile = fopen(tempfile, "wb+");
/* Copy first index records from old file to new file */
rewind(pFile); /* Old file back to start */
struct Record record; /* Store for a record */
for(int i = 0 ; iwriterecord(readrecord(&record, pFile), ptempfile);
writerecord(pnewrecord, ptempfile); /* Write the new record */
readrecord(&record,pFile); /* Skip the old record */
/* Copy the rest of the old file to the new file */
while(readrecord(&record,pFile))
writerecord(&record, ptempfile);
/* close the files */
if(fclose(pFile)==EOF)
printf("\n Failed to close %s", filename);
if(fclose(ptempfile)==EOF)
printf("\n Failed to close %s", tempfile);
if(remove(filename)) /* Delete the old file */
{
printf("\nRemoving the old file failed. Check file in %s", dirpath);
return;
}
/* Rename the new file same as original */
if(rename(tempfile, filename))
printf("\nRenaming the file copy failed. Check file in %s", dirpath);
}
/* Find a record */
/* Returns the index number of the record */
/* or -1 if the record is not found. */
int findrecord(struct Record *precord, FILE *pFile)
{
char name[MAXLEN];
printf("\nEnter the name for the record you wish to find: ");
getname(name);
rewind(pFile); /* Make sure we are at the start */
int index = 0; /* Index of current record */
while(true)
{
readrecord(precord, pFile);
if(feof(pFile)) /* If end-of-file was reached */
return -1; /* record not found */
if(!strcmp(name, precord->name))
break;
++index;
}
return index; /* Return record index */
}
Writing, reading and updating a binary file in C
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