I setup a breakpoint in my Go code with runtime.Breakpoint(), save the file (my editor, Atom with go-plus installed, runs go install . on save). Then I run Delve in terminal with dlv debug, and type continue after it starts.
When the breakpoint kicks in, I want to test a couple of things (basically to print reader's data via a bytes.Buffer). But, I get the following error
buf := new(bytes.Buffer): "1:5: expected 'EOF', found ':='"
and in general cannot do much more than print values.
Is it really not possible to do this sort of thing? I am used to Python's pdb where setting variables or calling functions is not a problem and I would expect Delve is capable of the same.
So, what am I doing wrong?
Not possible yet. Right now (2018-NOV) work is in progress on Delve, but unfinished.
Go runtime was changed recently to allow this kind of call. Delve have a Github issue tracking the progress of such feature, but is still experimental and incomplete.
I want to see the step by step execution of a fortran code.
I have the option of gdb but i want something more visual inside an editor, something like visual studio code, but faster so that I can execute it till a break point and then see the execution from that point onwards step-by-step.
Any recommendation apart from the traditional terminal gdb for the same purpose ?
There is a plugin for eclipse for fortran, based on CDT. It is called Photran and provides a graphical interface for gdb, in addition to other useful features like makefile support and generation and declaration lookup.
I've been using the JetBrains IDE AppCode for a few years now, but I've never had the need to pass command line arguments to the debugger before. As you probably know, in order to link the compiler with the necessary curses files, you have to include -lcurses in the command line to compile the program. The issue I'm having is that I'm not exactly sure how to correctly pass this parameter to the debugger. Thanks in advance.
A debugger should not need the list of libraries since all of the relevant information about linked libraries exists in the executable which is being debugged.
The interactive environment is VERY helpful for a programmer. However, it seems Go does not provide it. Is my understanding correct?
No, Go does not provide a REPL(read–eval–print loop).
However, as already mentioned, Go Playground is very handy. The Go Authors are also thinking about adding a feature-rich editor to it.
If you want something local, consider installing hsandbox. Running it simply with hsandbox go will split your terminal screen (with screen) where you can write code at the top and see its execution output at the bottom on every save.
There was a gotry among standard Go commands, which used to evaluate expressions (with an optional package name), and could be run like gotry 1+2 and gotry fmt 'Println("hello")' from shell. It is no longer available because not many people actually used it.
I have also seen third party projects for building a REPL for Go, but now I can only find links to two of them: igo and go-repl. How well do they work I don't know.
My two cents: Speed of compilation makes writing a REPL possible for Go, as it has also helped building the tools mentioned here, but the same speed makes REPL less necessary. Every time I want to test something in Go that I can't run in Playground I open a simple .go file and start coding and simply run the code. This will be even easier when the go command in Go 1 makes one-command build process possible and way easier.
UPDATE: Latest weekly release of Go added go command which can be used to very easily build a file: write your prog.go file and run go build prog.go && ./prog
UPDATE 2: With Go 1 you can directly run go programs with go run filename.go
UPDATE 3: gore is a new project which seems interesting.
Try motemen/gore
Yet another Go REPL that works nicely. Featured with line editing,
code completion, and more.
https://github.com/motemen/gore
You also have a recent (March 2013) project called gore from Sriram Srinivasan, which can be useful:
gore is a command-line evaluator for golang code -- a REPL without a loop, if you will.
It is a replacement for the go playground, while making it much easier to interactively try out bits of code: gore automatically supplies boiler-plate code such as import and package declarations and a main function wrapper.
Also, since it runs on your own computer, no code is rejected on security grounds (unlike go playground's safe sandbox mode).
If you're a Vim user, the vim-go plugin (https://github.com/fatih/vim-go) provides a command (GoRun) to run and print the output of the current buffer. You still have to include all the boilerplate code of a main Go file, but it still provides a convenient way to quickly test code snippets in your local environment.
Have you tried the Go Playground?
About the Go Playground
The Go Playground is a web service that runs on golang.org's servers.
The service receives a Go program, compiles, links, and runs the
program inside a sandbox, then returns the output.
The GoSpeccy project includes a builtin REPL of a restricted subset of the Go language. The implementation is using goeval.
No, but you can exploit the speed of compilation (as mentioned in other answers).
Have a look at rango that uses a generate-compile-run loop to mimic a REPL. You can also start it with imports and statements to begin an interactive session.
Gosh is the interactive Golang shell. The goal is to provide an easy-to-use interactive execution environment.
https://github.com/mkouhei/gosh
I've had some luck with the VSCode debugger, but it's fairly limited in so far as you cannot invoke function calls from the debug console Debug: Function Calls not supported #2225.
Basically you set a breakpoint after properly configuring your launch.json file. Then you can drill down on the left in the variables side bar and enter variable expressions an the debug console.
You may also like to try https://github.com/haya14busa/goplay
This enables you to run go code files from your terminal directly to the Go Playground
Please also check www.gorepl.com for go REPL and other REPLs
Go code can be run in a REPL-like way in Visual Studio Code with the Go extension and Code Runner extension. Click the Run triangle ▶ which is marked by the mouse cursor in the below screenshot to run the code and show the results in the Output pane at the bottom of Visual Studio Code.
When programming with Go Visual Studio Code will suggest additional Go extensions that can be installed to extend Visual Studio Code's functionality.
I have a process that changes its current directory, and I would like to know when and where it happens. How could I do that?
I tried setting a breakpoint in SetCurrentDirectoryA/SetCurrentDirectoryW with Visual Studio, but it does not work.
Are you debugging one of your own programs, or one that you don't have the source code for? The Visual Studio debugger isn't very friendly with regards to debugging no-source applications; in that case, I would recommend WinDbg or OllyDbg - or even skipping the debugger and write an instrumented logger using EasyHook.
EDIT:
Try setting a breakpoint at {,,kernel32.dll}_SetCurrentDirectoryA#4 - peculiar syntax and requires decorated names. Haven't tried it myself, but found it here. Google keywords: "visual studio breakpoint api" :)
You need to attach/debug the process using native code. If you by mistake are debugging using managed code you will not hit those breakpoints.
Your program may be changing directories using the msvcrt functions.
You should try placing breakpoints on these functions as well:
_chdir
_chdrive