cin and read(*,*) not waiting for kbd input in gdb

Jon Turney jon.turney@dronecode.org.uk
Fri Jan 17 15:40:00 GMT 2020


On 16/01/2020 21:02, Rockefeller, Harry wrote:
> Both the Fortran and cpp used to work correctly when run in gdb.

Thanks for reporting this problem.

I assume this means that this worked with gdb-8.1.1-1, but not with 
gdb-8.2.1-1 (Made available for testing 2019-03-21 [1], promoted to 
current 2020-01-07 [2])

Firstly, can I suggest that if a working gdb is important to you, you 
try test versions when they are available.  Wider testing helps me make 
good releases of gdb.

Secondly, can you try the recently made test release of gdb-8.3.1-1 [3], 
to see if this behaves differently?  If that doesn't help, you can 
downgrade to 8.1.1-1 for the moment...

[1] https://cygwin.com/ml/cygwin-announce/2019-03/msg00032.html
[2] https://cygwin.com/ml/cygwin/2020-01/msg00064.html
[3] https://cygwin.com/ml/cygwin-announce/2019-12/msg00033.html

> FWIW, Both Fortran and cpp work correctly, stopping for keyboard input, when run outside of gdb.
> 
> But now, code simply doesn't stop to take keyboard input inside gdb.
> 
> I've tried simplifying cpp problem with simple code.
> e.g.
> #include <iostream> // to enable terminal printout
> #include <cmath>    // pow function
> int main() {
>    float request_time_to_run(void);
>    float a=0.0f;
>    a = request_time_to_run();
>    printf ("a is %f\n", a);
> }
> float request_time_to_run() {
>    float tm = 0.0;        // Time duration (sec)
>    std::string ans = "";  // interactive answer for time duration
>    std::cout << "Supply the equivalent of runtime in seconds. \n";
>    std::cout << "Note: time=0 will stop main. \n";
>    std::cin >> ans;
>    if ( (int)(ans[0]) < 48 || (int)(ans[0] > 57) ) {
>      tm = 1.0;
>    } else {
>      int i;
>      int j = 0;
>      tm = 0.0;
>      for (i=ans.length() - 1; i>=0; i--) {
>        tm += ((int)(ans[i]) - 48) * pow( 10, j++);
>      }
>    }
>    return tm;
> }
> 

I'm not able to reproduce this problem.  Perhaps you can provide a 
similar transcript showing the steps to reproduce?

> $ gdb rockefeller.exe
> GNU gdb (GDB) (Cygwin 8.2.1-1) 8.2.1
> Copyright (C) 2018 Free Software Foundation, Inc.
> License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
> This is free software: you are free to change and redistribute it.
> There is NO WARRANTY, to the extent permitted by law.
> Type "show copying" and "show warranty" for details.
> This GDB was configured as "x86_64-pc-cygwin".
> Type "show configuration" for configuration details.
> For bug reporting instructions, please see:
> <http://www.gnu.org/software/gdb/bugs/>.
> Find the GDB manual and other documentation resources online at:
>     <http://www.gnu.org/software/gdb/documentation/>.
> 
> For help, type "help".
> Type "apropos word" to search for commands related to "word"...
> Reading symbols from rockefeller.exe...done.
> (gdb) b request_time_to_run()
> Breakpoint 1 at 0x1004010e8: file rockefeller.cpp, line 10.
> (gdb) r
> Starting program: /wip/rockefeller.exe
> 
> Thread 1 "rockefeller" hit Breakpoint 1, request_time_to_run () at rockefeller.cpp:10
> 10        float tm = 0.0;        // Time duration (sec)
> (gdb) n
> 11        std::string ans = "";  // interactive answer for time duration
> (gdb) n
> 12        std::cout << "Supply the equivalent of runtime in seconds. \n";
> (gdb) n
> Supply the equivalent of runtime in seconds.
> 13        std::cout << "Note: time=0 will stop main. \n";
> (gdb) n
> Note: time=0 will stop main.
> 14        std::cin >> ans;
> (gdb) n
> 1
> 15        if ( (int)(ans[0]) < 48 || (int)(ans[0] > 57) ) {
> (gdb) n
> 19          int j = 0;
> (gdb) c
> Continuing.
> a is 1.000000
> [Inferior 1 (process 12660) exited normally]


> But, simple stuff does run correctly in gdb stopping for terminal input at
>    std::cin >> ans;
> FWIW, for simple cpp above neither the cout nor the cin works directly (not running in gdb).

Although not related to gdb, that would be a serious cygwin bug.


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