Fread binary file dynamic size string [C]
- by Blackbinary
I've been working on this assignment, where I need to read in "records" and write them to a file, and then have the ability to read/find them later. On each run of the program, the user can decide to write a new record, or read an old record (either by Name or #)
The file is binary, here is its definition:
typedef struct{
char * name;
char * address;
short addressLength, nameLength;
int phoneNumber;
}employeeRecord;
employeeRecord record;
The way the program works, it will store the structure, then the name, then the address. Name and address are dynamically allocated, which is why it is necessary to read the structure first to find the size of the name and address, allocate memory for them, then read them into that memory.
For debugging purposes I have two programs at the moment. I have my file writing program, and file reading.
My actual problem is this, when I read a file I have written, i read in the structure, print out the phone # to make sure it works (which works fine), and then fread the name (now being able to use record.nameLength which reports the proper value too).
Fread however, does not return a usable name, it returns blank.
I see two problems, either I haven't written the name to the file correctly, or I haven't read it in correctly.
Here is how i write to the file: where fp is the file pointer. record.name is a proper value, so is record.nameLength. Also i am writing the name including the null terminator. (e.g. 'Jack\0')
fwrite(&record,sizeof record,1,fp);
fwrite(record.name,sizeof(char),record.nameLength,fp);
fwrite(record.address,sizeof(char),record.addressLength,fp);
And i then close the file.
here is how i read the file:
fp = fopen("employeeRecord","r");
fread(&record,sizeof record,1,fp);
printf("Number: %d\n",record.phoneNumber);
char *nameString = malloc(sizeof(char)*record.nameLength);
printf("\nName Length: %d",record.nameLength);
fread(nameString,sizeof(char),record.nameLength,fp);
printf("\nName: %s",nameString);
Notice there is some debug stuff in there (name length and number, both of which are correct). So i know the file opened properly, and I can use the name length fine. Why then is my output blank, or a newline, or something like that? (The output is just Name: with nothing after it, and program finishes just fine)
Thanks for the help.
