Compiling in Emacs

1. The "Normal" Way to Compile C++ Code in Linux(?)
2. The Emacs Way
3. Handling makefiles that change directories
4. Beyond Compilation

1 The "Normal" Way to Compile C++ Code in Linux(?)

Open two terminals, one for compilation, the other for editing.
Run compile command in one terminal and redirect compilation output to a file.
Open the file and manually screen the output.
Once spotted a compilation error,
1. Remember the file name and line number
2. Switch to the other terminal
3. Open corresponding file and jump to the designated line.
Sometimes, spend a lot of time debugging since forget to save before compile

2 The Emacs Way

2.1 Run `M-x compile` when you want to compile

You should run the command with the current path the directory makefile. Usually, opening the makefile will do the job

2.2 Press <enter>

Since I configured the default compile command to exactly what I want, no need to type the command for compilation.

2.3 Errors highlighted in a new buffer

2.4 Jump to the error spot

C-x ` (Or just a mouse click).

2.5 Fix error and `M-x recompile`.

2.6 You will not forget to save your code before compilation

Emacs will prompt you if you hadn't do that before (re)compile.

3 Handling makefiles that change directories

3.1 Some makefiles are annoying since there are "cd" commands.

For example:

%.subdir:
  @if ([ ! -d $(patsubst %.subdir,%,$@) ]); then \
      $(ECHO) "*** Error " $(patsubst %.subdir,%,$@);\
      exit 1; \
  fi;
  @cd $(patsubst %.subdir,%,$@); \
  $(ECHO) "Checking `pwd` for work"; \
  $(MAKE_COMMAND)

3.2 Consequently, C-x ` can not locate errors correctly

since the files are not where shown in the compilation buffer.

3.3 The solution

is straightforward: update the "default-directory" to where the compilation actually happened.

For example, in this example, I know that string "Checking xxx for work" indicates a directory change. So, all that I need to do is to search that backward from the bottom of compilation buffer.

(setq compile-command "make SWATCA=t"
      compilation-scroll-output t)

(define-key compilation-mode-map "r" 'lgfang-relocate-make)
(defun lgfang-relocate-make ()
  "Plexus specific: relocate default-directory according to last
'Checking ... for work'. Dirty but works"
  (interactive)
  (save-excursion
    (goto-char (point-max))
    (message "Relocate `make' to: %s"
             (setq default-directory
                   (replace-regexp-in-string
                    "Checking *" ""
                    (replace-regexp-in-string
                     " *for work *" ""
                     (buffer-substring
                      (re-search-backward "Checking .* for work")
                      (progn (end-of-line)(point)))))))))

3.4 With above code, every time confronted with such issue, I just press "r" to "relocate"

4 Beyond Compilation

In fact, the compile command can be used to do other things. For instance Unit Test.