C Video Tutorial 11
In this part of the C Video Tutorial I will provide C File IO examples. I’ll cover C Text File IO in this tutorial and the Binary File IO functions in the next part.
I specifically cover the following topics: FILE Data type, fopen(), fputs(), fseek(), ftell(), fgets(), fclose(), fscanf(), puts(), fprintf(), Different Ways to Access Files, and more. All of the code used is available below the video.
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Code From the Video
CTutorial11.c
#include <stdio.h>
#include <stdlib.h>
// C provides numerous methods for working with files
// A file is just a block of memory with a name
// The file can be stored across many blocks in memory,
// but the C compiler acts as if it is in sequence.
// In this tutorial I will cover how to work with files
// if we represent them as text files. next time I'll cover how
// to use Binary File I/O
/*
int main(){
int randomNumber;
// Will store the pointer to the file
FILE *pFile;
// Opens a text file so we can write data to it.
// It returns a pointer to the file
// w - If a file doesn't exist create it. If it does overwrite it
// a - Open or create text file and append to original content
// r - Open a file to read from it
// r+ - Open for reading and writing
// w+ - Open or create, delete original and read and write
// a+ - Open or create, append for writing and reading
pFile = fopen("randomnumbers.txt", "w");
// If the file wasn't opened a 1 is returned from fopen()
if(!pFile){
printf("Error : Couldn't Write to File\n");
return 1;
}
// Print 10 random numbers to the file
for(int i = 0; i < 10; i++){
randomNumber = rand() % 100;
// fprintf() prints to the file supplied just like
// printf() prints to the screen
fprintf(pFile, "%d\n", randomNumber);
}
printf("Success Writing to File\n");
// Closes the text file
// This must be done or eventually the program will run
// out of file handlers or memory
if(fclose(pFile) != 0)
printf("Error : File Not Closed\n");
return 0;
}
*/
int main(){
// Defining that we only expect there to be a maximum of 1,000
// characters per lines read.
char buffer[1000];
FILE *pFile;
// Opens the file for reading
pFile = fopen("randomnumbers.txt", "r");
// fopen returns 1 if an error occurred
if(!pFile){
printf("Error : Couldn't Read the File\n");
return 1;
}
// fgets() reads up to 1,000 characters per line until
// fgets() returns the value of NULL when it reaches
// the end of the file.
// while(fgets(buffer, 1000, pFile) != NULL){
// printf("%s", buffer);
// }
// You can also read from a file using fscanf
// You pass the file, data type to read and the buffer
// to store it in. You can check for valid data because
// fscanf() returns a number other then 1 if it isn't
// a string
while(fscanf(pFile, "%s", buffer) == 1){
// Puts outputs the string plus a newline.
// Returns a nonnegative integer if it was successful
// and EOF if there was an error
puts(buffer);
}
printf("Success Reading from File\n");
// Closes the text file
if(fclose(pFile) != 0)
printf("Error : File Not Closed\n");
return 0;
}
CTutorial11_2.c
#include <stdio.h>
#include <stdlib.h>
int main(){
FILE * pFile;
pFile = fopen("randomwords.txt", "r+");
char buffer[1000];
// If the file wasn't opened a 1 is returned from fopen()
if(!pFile){
printf("Error : Couldn't Write to File\n");
return 1;
}
fputs("Messing With Strings", pFile);
// Move 12 spaces from the beginning of the file
// SEEK_SET - Move starting from the beginning of the file
// SEEK_CUR - Move based off of the current position in the file
// SEEK_END - Move based off of starting at the end of the file
fseek(pFile, 12, SEEK_SET);
// Overwrite characters starting at char number 12
fputs(" Files ", pFile);
printf("Success Writing to File\n");
// Move back to the beginning of the file
fseek(pFile, 0, SEEK_SET);
// 2 : Move to the end of the file
fseek(pFile, 0, SEEK_END);
// ftell() tells you how far you are currently from the
// beginning of the file
long numberOfBytes = ftell(pFile);
printf("Number of Bytes in File : %d\n", numberOfBytes);
// 3 : This moves backwards 20 bytes in the file
fseek(pFile, -20, SEEK_CUR);
while(fgets(buffer, 1000, pFile) != NULL){
printf("%s", buffer);
}
printf("\n");
// Closes the text file
// This must be done or eventually the program will run
// out of file handlers or memory
if(fclose(pFile) != 0)
printf("Error : File Not Closed\n");
return 0;
}
Thank you for the tutorials in C!
I enjoyed your Java lessons – they helped me quite a bit in school. I am now taking a Discrete Structures course where I must implement assignments in the C programming language and was pleasantly surprised to find these videos from a trusted source.
Point of clarification:
In the commented section of the first main function, I notice it states that fopen() returns a ‘1’ if it is unsuccessful. Is this correct? Other sources state that it returns NULL or a ‘0’ if it is unsuccessful.
Thank you in advance!
Yes Null is returned. Sorry about that error. I’m very happy that you are enjoying the tutorial 🙂