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Why does getw return -1 when trying to read a character?


Why does getw return -1 when trying to read a character?

By : A Doe
Date : October 19 2020, 06:10 PM
will be helpful for those in need You are writing one byte to the file, but then try to read sizeof(int) bytes back from it. getw() returns EOF because of that, and the value of EOF is -1.
For this reason, when using getw() you should examine the file handle using ferror() to be able to tell whether the value getw() returned is the value read from the file or an error code.
code :
int x = getc(fp);
if (x == EOF) {
    fputs("Error reading from file.\n", stderr);
} else {
    printf("%d\n",x);
}


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C++ having cin read a return character

C++ having cin read a return character


By : David
Date : March 29 2020, 07:55 AM
Any of those help I was wondering how to use cin so that if the user does not enter in any value and just pushes ENTER that cin will recognize this as valid input. , You will probably want to try std::getline:
code :
#include <iostream>
#include <string>

std::string line;
std::getline( std::cin, line );
if( line.empty() ) ...
I am writing 0 to 255 ascii character and trying to read it character by characte but cant read after 25th character

I am writing 0 to 255 ascii character and trying to read it character by characte but cant read after 25th character


By : Amal MK
Date : March 29 2020, 07:55 AM
may help you . The reason why you can't read the 26th character is because its value is 26. And that is interpreted in textfiles as an end-of-file marker. You must open your file as binary ,then it will work.
How to read a character in OCaml without a return key?

How to read a character in OCaml without a return key?


By : W.Eddie
Date : March 29 2020, 07:55 AM
Hope this helps Handling input in full lines is easy. Handling it a character at a time is a little bit system dependent. If you're on a Unix-like system you should be able to do this using the Unix module:
code :
let get1char () =
    let termio = Unix.tcgetattr Unix.stdin in
    let () =
        Unix.tcsetattr Unix.stdin Unix.TCSADRAIN
            { termio with Unix.c_icanon = false } in
    let res = input_char stdin in
    Unix.tcsetattr Unix.stdin Unix.TCSADRAIN termio;
    res
Cannot understand this output from getw

Cannot understand this output from getw


By : user2168212
Date : March 29 2020, 07:55 AM
will help you First, using %u to print an int is undefined behavior. Either use %d or cast a to unsigned in your printf call.
Second, getw() reads in a word (or sizeof(int) bytes) from the stream. It performs binary I/O, not formatted I/O.
Read problems using getw()

Read problems using getw()


By : user2274395
Date : March 29 2020, 07:55 AM
I wish did fix the issue. The int getw(FILE *) function is for reading an integer directly from the bytes of a file, not for reading an integer from the textual contents of a file.
If you wish to read integers from a file, one by one, use fscanf instead:
code :
FILE *in_file = fopen("file1.txt", "r");
FILE *out_file = fopen("file2.txt", "w");
int num;
while (fscanf(in_file, "%d", &num) == 1) {
    if (is_prime(num)) {
        fprintf(out_file, "%d\n", num);
    }
}
fclose(in_file);
fclose(out_file);
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