File handling is a very common task. Here are snippets of code I use to perform various file handling operations in Python, Java and C.
Reading a file in Python
Reading a file at once
try:
with open("/path/to/file/filename.txt", "r") as f:
text = f.read()
# text is a string which contains all the text in the file.
# this may cause problems with very big files.
# do something with text
print text
except IOError as e:
print "IOError: %s: %s" % (e.filename, e.strerror)
Reading a file line by line
try:
with open("/path/to/file/filename.txt", "r") as f:
for line in f:
# line is a string
# a newline character (\n) is present at the end of the string
# and is only omitted on the last line of the file if the
# file doesn't end in a newline.
# do something with line
print line
except IOError as e:
print "IOError: %s: %s" % (e.filename, e.strerror)
Reading a file word by word
try:
with open("/path/to/file/filename.txt", "r") as f:
for line in f:
for word in line.split():
# do something with word
print word
except IOError as e:
print "IOError: %s: %s" % (e.filename, e.strerror)
Reading a file character by character
try:
with open("/path/to/file/filename.txt", "r") as f:
while True:
character = f.read(1)
if character:
# do something with character
print character
else:
# end-of-file reached
break
except IOError as e:
print "IOError: %s: %s" % (e.filename, e.strerror)
Writing a file in Python
with open("/path/to/file/filename.txt", "w") as f:
# write to the file using f.write()
f.write('Whatever you want to write.\n')
f.write('Really, anything.\n')
Reading a file in Java
Reading a file at once
This question on Stack Overflow shows various ways to do this.
Reading a file line by line
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.FileNotFoundException;
import java.util.Scanner;
public class FileLL {
public static void main(String[] args) {
Scanner s = null;
try {
s = new Scanner(new BufferedReader(new FileReader("/path/to/file/filename.txt")));
while (s.hasNext()) {
String line = s.nextLine();
// line does not contain a newline (\n) at the end.
// do something with line
System.out.print(line);
}
} catch (FileNotFoundException e) {
System.err.println("Can't open input file!");
System.err.println(e.getMessage());
} finally {
if (s != null) {
s.close();
}
}
}
}
Reading a file word by word
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.FileNotFoundException;
import java.util.Scanner;
public class FileWW {
public static void main(String[] args) {
Scanner s = null;
try {
s = new Scanner(new BufferedReader(new FileReader("/path/to/file/filename.txt")));
while (s.hasNext()) {
String word = s.next();
// do something with the word
System.out.println(word);
}
} catch (FileNotFoundException e) {
System.err.println("Can't open input file!");
System.err.println(e.getMessage());
} finally {
if (s != null) {
s.close();
}
}
}
}
Reading a file character by character
import java.io.FileReader;
import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.IOException;
public class FileCC {
public static void main(String[] args) throws IOException {
BufferedReader br = null;
try {
br = new BufferedReader(new FileReader("/path/to/file/filename.txt"));
int ch;
while ((ch = br.read()) != -1) {
char character = (char) ch;
// do something with the character.
System.out.print(character);
}
} catch (FileNotFoundException e) {
System.err.println("Can't open input file!");
System.err.println(e.getMessage());
} finally {
if (br != null) {
br.close();
}
}
}
}
Writing a file in Java
import java.io.FileWriter;
import java.io.BufferedWriter;
import java.io.IOException;
public class FileW {
public static void main(String[] args) throws IOException {
BufferedWriter bw = new BufferedWriter(new FileWriter("/path/to/file/filename.txt"));
bw.write("Whatever you want to write.\n");
bw.write("Really, anything.\n");
bw.close();
}
}
Reading a file in C
Reading a file at once
I don’t know of a straightforward way to do this. Feel free to chime in the comments if you know one.
Reading a file line by line
#include <stdlib.h>
#include <stdio.h>
int main() {
FILE *fp = fopen("/path/to/file/filename.txt", "r");
if (fp == NULL) {
fprintf(stderr, "Can't open input file!\n");
exit(1);
}
char line[1024];
// assuming no line in the file is longer than 1024 characters.
while (fgets(line, sizeof line, fp) != NULL) {
// line contains a newline (\n) at the end
// except maybe for the last line of the file
// if the file doesn't end with a newline
// do something with line
printf("%s\n", line);
}
fclose(fp);
return 0;
}
Reading a file word by word
#include <stdlib.h>
#include <stdio.h>
int main() {
FILE *fp = fopen("/path/to/file/filename.txt", "r");
if (fp == NULL) {
fprintf(stderr, "Can't open input file!\n");
exit(1);
}
char word[64];
// assuming no word in the file is longer than 64 characters.
while (fscanf(fp, "%64s", word) != EOF) {
// do something with word
printf("%s\n", word);
}
fclose(fp);
return 0;
}
Reading a file character by character
#include <stdlib.h>
#include <stdio.h>
int main() {
FILE *fp = fopen("/path/to/file/filename.txt", "r");
if (fp == NULL) {
fprintf(stderr, "Can't open input file!\n");
exit(1);
}
int ch;
while ((ch = fgetc(fp)) != EOF) {
char character = (char) ch;
// do something with character
printf("%c", character);
}
fclose(fp);
return 0;
}
Writing a file in C
#include <stdlib.h>
#include <stdio.h>
int main() {
FILE *fp = fopen("/path/to/file/filename.txt", "w");
if (fp == NULL) {
fprintf(stderr, "Can't open input file!\n");
exit(1);
}
fprintf(fp, "Whatever you want to write.\n");
fprintf(fp, "Really, anything.\n");
fclose(fp);
return 0;
}
