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[\<- Notes 02/07](02-07.md)
---
# Files Continued
## Binary Files
- Use Binary Files when no need for a human to read the file
- Converting information into a stream of characters and back into internal format (in this case) is wasting computational cycles and time
- Files containing binary numbers that are the computer's internal representation of each file component
- Created by executing a program that stores directly in the computer's internal representation of each file component
- Actually just a stream of zeros and ones and cannot be read with a text editor
- Example `char x = 2` in memory is `00000010`
- Example `short x = 2` in memory is `0000000000000010`
- Example `int x = 2` in memory is `00000000000000000000000000000010`
- To open a binary file for reading:
```
FILE *infp;
if((infp = fopen("data.txt", "rb")) == NULL) printf("cannot open the file data.txt\n");
```
- The file is always open for reading from the beginning
- The file name can also be stored in a string
- To read from a binary file:
```
ret = fread(&x, sizeof(int), 1, infp);
```
- The file is read sequentially
- Consecutive calls to fread will read consecutive elements from the file
- The next integer is placed into the variable x
- Function fread returns the number of elements read
- At the end of the file, fread returns -1
- To open a binary file for writing from the beginning:
```
FILE *outfp;
if((outfp = fopen("data.txt", "wb")) == NULL) printf("cannot open the file data.txt\n")
```
- To open a binary file for writing from the end (append):
```
FILE *outfp;
if((outfp = fopen("data.txt", "ab")) == NULL) printf("cannot open the file data.txt\n")
```
- To write to a binary file:
```
ret = fwrite(&x, sizeof(int), 1, outfp);
```
- The contents of variable x is written to the file
- The file is written sequentially
- function fwrite returns the number of elements written
- To close a binary file:
```
fclose(infp);
fclose(outfp);
```
- **Files cannot be written or read unless specifically set to do so**
- cannot read when open to write and vice versa
- must close the file if currently open for reading before opening for writing and vice versa
List of Functions to Learn/Remember:
```
fopen, fclose
fprintf, fscanf
fgets
fread, fwrite
fpurge
fflush
fseek
```
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