Logo

Programming-Idioms

  • Python
  • Scala

Idiom #58 Extract file content to a string

Create the string lines from the content of the file with filename f.

import scala.io.Source
val lines = Source.fromFile(filename).getLines().mkString("\n")
lines = open(f).read()

For more complicated file operations, use a context manager with with
with open(f) as fo:
    lines = fo.read()

The with statement creates a contextmanager, which automatically handles closing the file for you when you're done. Without this, you should be manually closing file objects so that you are not relying on the garbage collector to do this for you.
#include <sys/mman.h>
#include <sys/stat.h>
#include <fcntl.h>
int err = 0;
int fd = 0;
void * ptr = NULL;
struct stat st;
if ((fd = open (f, O_RDONLY))
&& (err = fstat (fd, &st)) == 0
&& (ptr = mmap (NULL, st.st_size, PROT_READ, MAP_PRIVATE, fd, 0)) != -1) {
    const char * lines = ptr;
    puts (lines);
    munmap (ptr, st.st_size);
    close (fd);
}

Mapping the whole file into the process address space avoids allocating memory.
New implementation...
< > ⌨
programming-idioms.org 
val lines = Source.fromFile(filename).getLines().mkString("\n")
lines = open(f).read()
with open(f) as fo:
    lines = fo.read()
int err = 0;
int fd = 0;
void * ptr = NULL;
struct stat st;
if ((fd = open (f, O_RDONLY))
&& (err = fstat (fd, &st)) == 0
&& (ptr = mmap (NULL, st.st_size, PROT_READ, MAP_PRIVATE, fd, 0)) != -1) {
    const char * lines = ptr;
    puts (lines);
    munmap (ptr, st.st_size);
    close (fd);
}
FILE *file;
size_t len=0;
char *lines;
assert(file=fopen(f,"rb"));
assert(lines=malloc(sizeof(char)));

while(!feof(file))
{
	assert(lines=realloc(lines,(len+0x1000)*sizeof(char)));
	len+=fread(lines,1,0x1000,file);
}

assert(lines=realloc(lines,len*sizeof(char)));

(def lines (slurp f))
std::string fromFile(std::string _f)
{
    std::ifstream t(_f);
    t.seekg(0, std::ios::end);
    size_t size = t.tellg();
    std::string buffer(size, ' ');
    t.seekg(0);
    t.read(&buffer[0], size); 
}
string lines = File.ReadAllText(f);
auto lines = f.readText;
string lines = cast(string) read(f, size_t.max);
var lines = new File(f).readAsStringSync();
lines = File.read!(f)
{ok, Lines} = file:read_file(F).
program p
   character(len=:),allocatable :: s
   open(unit=10,file='myfile',access='stream')
   inquire(10,size=i)
   allocate(character(len=i) :: s)
   read(10)(s(j:j),j=1,i)
   write(*,*)s
end program p

b, err := os.ReadFile(f)
if err != nil {
	// Handle error...
}
lines := string(b)
do lines <- readFile f; putStr lines
fs.readFile(f, (err, lines) => {
    if (err) {
        // Handle error...
    }

    // Work with `lines` here.
}
File F = new File(f);
try (Scanner s = new Scanner(F)) {
    s.useDelimiter("\\R");
    String n = lineSeparator(),
           lines = s.tokens()
                    .collect(joining(n));
}
byte[] encoded = Files.readAllBytes(Paths.get(f));
String lines = new String(encoded, StandardCharsets.UTF_8);
File(f).readText()
(defvar *lines*
   (with-open-file (stream f)
      (let ((contents (make-string (file-length stream))))
            (read-sequence contents stream)
      :return contents)))
(with-open-file (stream f)
  (uiop:slurp-stream-string stream))
lines = io.input(f):read('a')
NSString *lines=[NSString stringWithContentsOfFile:f encoding:e error:NULL];

$lines = file_get_contents('f');
if ($lines === false) {
    // handle error...
}
var
 _lines, _f: String;
 SL: TStringList;
begin
  SL := TStringList.Create;
  SL.LoadFromFile(_f);
  _lines := SL.Text;
  SL.Free;
end;
open my $fh, '<', $f;
my $lines = do { local $/; <$fh> };
close $fh;
lines = File.read(f)
let lines = fs::read_to_string(f).expect("Can't read file.");
let mut file = File::open(f)?;
let mut lines = String::new();
file.read_to_string(&mut lines)?;
| lines |
lines := f asFilename readStream upToEnd.
Dim lines = IO.File.ReadAllText(f)