I have a text file named test.txt
I want to write a C program that can read this file and print the content to the console (assume the file contains only ASCII text).
I don't know how to get the size of my string variable. Like this:
char str[999];
FILE * file;
file = fopen( "test.txt" , "r");
if (file) {
while (fscanf(file, "%s", str)!=EOF)
printf("%s",str);
fclose(file);
}
The size 999
doesn't work because the string returned by fscanf
can be larger than that. How can I solve this?
The simplest way is to read a character, and print it right after reading:
int c;
FILE *file;
file = fopen("test.txt", "r");
if (file) {
while ((c = getc(file)) != EOF)
putchar(c);
fclose(file);
}
c
is int
above, since EOF
is a negative number, and a plain char
may be unsigned
.
If you want to read the file in chunks, but without dynamic memory allocation, you can do:
#define CHUNK 1024 /* read 1024 bytes at a time */
char buf[CHUNK];
FILE *file;
size_t nread;
file = fopen("test.txt", "r");
if (file) {
while ((nread = fread(buf, 1, sizeof buf, file)) > 0)
fwrite(buf, 1, nread, stdout);
if (ferror(file)) {
/* deal with error */
}
fclose(file);
}
The second method above is essentially how you will read a file with a dynamically allocated array:
char *buf = malloc(chunk);
if (buf == NULL) {
/* deal with malloc() failure */
}
/* otherwise do this. Note 'chunk' instead of 'sizeof buf' */
while ((nread = fread(buf, 1, chunk, file)) > 0) {
/* as above */
}
Your method of fscanf()
with %s
as format loses information about whitespace in the file, so it is not exactly copying a file to stdout
.