Executable from x86_64-w64-mingw32-gcc.exe waits for input before prompt in Cygwin terminal but not Win Command Prompt

Executable from x86_64-w64-mingw32-gcc.exe waits for input before prompt in Cygwin terminal but not Win Command Prompt

[Randy Decker]

# Brief problem description
# C source file  -      'printf("Test");' added as diagnostics
# Source compiles and executes in Ubuntu
# Executable compiled in cygwin terminal OK in command prompt W8.1
# - Also OK in another machine running Windows 8.1
# Same executable in cygwin term waits for input before usage hint

FROM CYGWIN64 TERMINAL
Randy@Hartford ~
$ cat countbytes.c  
/* This program counts the number of bytes in a C source file.
   The program prompts the user for a file name and then concatenates
   the ".c" extension to this name. It uses the function getc to read
   the characters.
   program from "Applications Programming in ANSI C"  by
    Hohnsonbaugh & Kalin
*/
#include<stdlib.h>
#include<stdio.h>
#include<string.h>
main( )
{
    FILE* fptr;
    char extension[] = ".c";
    int char_count;
    printf("Test");
    printf("\n\n\tFile name (NO extension):\t");
    char file_name[FILENAME_MAX];  /* defined in stdio.h*/
    scanf("%s",file_name);
    strcat(file_name,extension);
    fptr=fopen(file_name,"rb");
    for(char_count=0; getc(fptr) !=EOF; ++char_count);
    printf("\n\tByte size:\t%d", char_count);
    printf("\n");
    fclose(fptr);
    return EXIT_SUCCESS;
}

# Confirm Countbytes.exe not yet here
Randy@Hartford ~
$ ls -a
.                     .swp                          myhello.exe
.$$$                  countbytes.c                  myhello2.exe
..                    countem.exe                   myhelloworld.c
.bash_history         countem3.exe                  testc.c
.bash_profile         countemm.exe                  testit.exe
.bash_profile_temp    countemm2.exe                 testittestc.exe
.bash_profileWin.txt  countOnUbuntu.txt             testtext.txt
.bashrc               cygwinResults.txt             welcome.exe
.bashrc_ORG           Hello.c                       x86_64-w64-mingw32-gcc.exe
.inputrc              HelloFromUnix.c
.profile              HelloFromUnix-PFEvsNotepad.c
# Show alias
Randy@Hartford ~
$ alias
alias gcc='C:/cygwin64/bin/x86_64-w64-mingw32-gcc.exe'

# Compile the program
Randy@Hartford ~
$ gcc -o countbytes countbytes.c

# Verify countbytes.exe now exists
Randy@Hartford ~
$ ls
countbytes.c       cygwinResults.txt             Progress_Notes.txt
->countbytes.exe     Hello.c                       testc.c
countem.exe        HelloFromUnix.c               testit.exe
countem3.exe       HelloFromUnix-PFEvsNotepad.c  testittestc.exe
countemm.exe       myhello.exe                   testtext.txt
countemm2.exe      myhello2.exe                  welcome.exe
countOnUbuntu.txt  myhelloworld.c                x86_64-w64-mingw32-gcc.exe

# Execute the output in cygwin64 terminal.  Program waits with no output
# Until enter is pressed on a non blank line.
Randy@Hartford ~
$ ./countbytes
countbytes
Test
        File name (NO extension):
        Byte size:      865
Randy@Hartford ~
# Demonstrate same files as Cygwin64 Terminal
FROM WINDOWS 8.1 COMMAND PROMPT
 Directory of C:\cygwin64\home\Randy
[.]                            [..]
.$$$                           .bashrc
.bashrc_ORG                    .bash_history
.bash_profile                  .bash_profileWin.txt
.bash_profile_temp             .inputrc
.profile                       .swp
countbytes.c                   ->countbytes.exe
countem.exe                    countem3.exe
countemm.exe                   countemm2.exe
countOnUbuntu.txt              cygwinResults.txt
Hello.c                        HelloFromUnix-PFEvsNotepad.c
HelloFromUnix.c                myhello.exe
myhello2.exe                   myhelloworld.c
Progress_Notes.txt             testc.c
testit.exe                     testittestc.exe
testtext.txt                   welcome.exe
x86_64-w64-mingw32-gcc.exe
              31 File(s)      1,289,107 bytes
               2 Dir(s)  142,941,614,080 bytes free
# Execute the output in Windows command prompt terminal.  
# Program PRINTS "       File name (NO extension):"
# then waits Until filename is entered.
# NOTE: Execution of same code in Ubuntu 14.4 works like this.
C:\cygwin64\home\Randy>countbytes
Test
        File name (NO extension):       countbytes
        Byte size:      865
C:\cygwin64\home\Randy>

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Re: Executable from x86_64-w64-mingw32-gcc.exe waits for input before prompt in Cygwin terminal but not Win Command Prompt

[Corinna Vinschen]

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On Apr 11 20:15, Randy Decker wrote:
> # Brief problem description
> # C source file  -      'printf("Test");' added as diagnostics
> # Source compiles and executes in Ubuntu
> # Executable compiled in cygwin terminal OK in command prompt W8.1
> # - Also OK in another machine running Windows 8.1
> # Same executable in cygwin term waits for input before usage hint

It's a buffering problem.  The Cygwin terminal is using a pty which is
implemented using Named Pipes for stdio descriptors under the hood.  The
Windows libraries go into full buffered stdio mode.  One workaround is
an explicit call to fflush(stdout) before asking for input.


Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Maintainer                 cygwin AT cygwin DOT com
Red Hat

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