C puts() without newline

Question

I currently have this program that prints a text file on the console, but every line has an extra new line below it. if the text was

hello world

it would output hello

world

the code is this

#include <iostream>
#include <stdio.h>
#include <string.h>
using namespace std;
int _tmain(int argc, _TCHAR* argv[])
{
    FILE* fp;
    char input[80], ch = 'a';
    char key[] = "exit\n";
    int q;

    fp = fopen("c:\\users\\kostas\\desktop\\original.txt", "r+");

    while (!feof(fp)) {
        fgets(input, 80, fp);
        puts(input);
    }
    fclose(fp);

    return 0;
}

Pentateuch

Isn't iostream a C++ -only library and using a C++ -only keyword? – Juggins

Answer 1

puts() adds the newline character by the library specification. You can use printf instead, where you can control what gets printed with a format string:

printf("%s", input);

Deshabille

That "%s" instead of just using "printf(input);" is critical, lest any percent signs in input crash your program. – Fabrikoid

calling printf with "%s" is less efficient than fputs, but you probably don't care – Gallardo

@portforwardpodcast Compiler do change printf("%s",sting) to fputs(string,stdout), when you enalbe optimization, at least gcc does this. Some compiler maybe change it to fwrite() which is faster when you know the string lenght. – Rootstock

Why not just use the answer below? – Electrical

@Rootstock when did it do that? I don't see this transformation being done with any version of GCC I have available. I think the main issue is getting the stdout at the point of optimization. – Danelaw

@DanM. You are correct, my example was wrong, but in case when you have "%s\n" as format string gcc will replace it with puts(). Try to compile main(){printf("%s\n","");} with gcc <input file>. – Rootstock

@Rootstock but this question is about no newline specifically ;P – Danelaw

Answer 2

Typically one would use fputs() instead of puts() to omit the newline. In your code, the

puts(input);

would become:

fputs(input, stdout);

Fabrikoid

You could use printf() as well, but with a small amount of added overhead :-) – Fabrikoid

I'm glad I found this answer, as I didn't want to have the overhead of printf – Sissified

In fact, printf("%s", s) have no overhead over fputs(input, stdout), but fputs looks clean. – Hedgepeth

The printf("%s", s) has to parse the format string, which is definitely less overhead than a system call - but have you seen the code for parsing the format string? That's definitely overhead. q.v. code.woboq.org/userspace/glibc/stdio-common/… – Fabrikoid

@AlexNorth-Keys if you printf with newline, gcc will turn it into puts. godbolt.org/z/784dEvnjP – Telesis

Well, wait long enough and gcc might turn it into some more efficient quantum computed thing. Compiler magic marches on, although this often impedes debugging. – Fabrikoid

But it won't when using printf("%s", ...) without a newline, which was the original question: godbolt.org/z/h4jWeobY6 So fputs(s, stdout) really is the right answer here over printf("%s", s). – Tubercle

Answer 3

You can also write a custom puts function:

#include <stdio.h>

int my_puts(char const s[static 1]) {
    for (size_t i = 0; s[i]; ++i)
        if (putchar(s[i]) == EOF) return EOF;

    return 0;
}

int main() {
    my_puts("testing ");
    my_puts("C puts() without ");
    my_puts("newline");

    return 0;
}

Output:

testing C puts() without newline

Quotable

Answer 4

This should work:

#include<stdio.h>
void put_s(char* s){
    while(*s) putchar(*s++);
}

Just for the sakes of having more examples, here is another one involving recursion:

#include<stdio.h>
void put_s(char* s){
    if(!*s) return;
    putchar(*s);
    put_s(s+1);
}

Note: I noticed that your code wouldn't compile, because of the #include<iostream> and the using namespace std;.

Juggins

It works but could be quite inefficient if stdout is not buffered. – Kunin