Auto format messy code

Question

I am currently learning C++ and I am in the process of configuring Emacs as my C++ IDE. I am reading a PDF guide and copying code into my Emacs buffer. However upon pasting the code the formatting is incorrect which is what I expected.

For example:

  int count_x(char
∗
p, char x)
//
count the number of occurrences of x in p[]
//
p is assumed to point to a zero-ter minated array of char (or to nothing)
{
if (p==nullptr) return 0;
int count = 0;
for (;
∗
p!=0; ++p)
if (
∗
p==x)
++count;
return count;
}

How can I reformat the above code to look like this:

int count_x(char* p, char x)
      // count the number of occurrences of x in p[]
      // p is assumed to point to a zero-terminated array of char (or to nothing)
{
    if(p==nullptr) return 0;
    int count = 0;
    for(; *p!=0; ++p)
     if(*p==x)
          ++count;
    return count;
}

Thanks!

Answer 1

The code you posted has several issues which needs to be fixed.
I will explain a semiautomatic method. This will enable you to fix code which has different issues, with the same method.

1. This code is no valid c source code:
   1. the obvious: comment lines are not marked as comments. This is fixed easy with search and replace.
      Type: M-x query-replace-regexp RET // C-q C-j RET // RET !.
      Explanation: with this input you replace the string "//\n" with "//", eventually putting comment and comment markers on the same line.
      C-q means: press Control and q this quotes the next character. C-j means: insert a linefeed character.
   2. The not so obvious issue: your * is not a asterisk but some unicode character which a c-compiler does not recognize. Go with your cursor on an * and enter M-x describe-char. You have to replace this unicode-* with an ascii-*. To do this (and also, remove the newlines before and after it), do the following:
      • highlight (i.e.: mark, select) just the * in your code and copy it to kill ring with M-w.
      • then type: M-x query-replace-regexp RET C-q C-j \ C-y C-q C-j RET * RET !
2. now you have valid c-source code and you can use an automatic tool to prettify your code. The tool I describe here is clang-format.
   1. install the software clang-format on your computer (with Linux (Debian and Ubuntu like distributions) it is done with: sudo apt-get install clang-format)
   2. Install the package clang-format from melpa.
      More documentation about package management in Emacs here.
   3. Insert following line into your emacs configuration (e.g. init.el):
      (require 'clang-format) For further configuration of clang-format see here and here.
   4. Use M-x clang-format-buffer to prettify the whole code.

If you copy code from your book again, then verify it is valid c-source code. If not, then use steps from 1. to get valid c-source code.
Afterwards you only need to do step 2.4. to prettify your code.

Steps from 1. could be automated, but your problem is very special.