How to get the number of the output of `vimgrep`

Question

I wrote a vim-script function, which allows me to grep a keyword in my project.

function! CustomGrep(...)
    if a:0 == 0
        silent vimgrep <cword> **/*.h **/*.hpp **/*.c **/*.cpp
    else
        silent execute 'vimgrep' a:1 '**/*.h **/*.hpp **/*.c **/*.cpp'
    endif
    "cope
endfunction

Now I want to write another function, which can replace a keyword:

function! CustomReplace(target, newWord)
    call CustomGrep(a:target)
    " loop --- how to loop?
    execute 's/'.a:target.'/'.a:newWord.'/gc'
    cnext
    " end loop
endfunction

Obviously, I need a loop in the function, which looks like:

let cnt = CustomGrep(a:target)
for from 1 to cnt
execute 's/'.a:target.'/'.a:newWord.'/gc'
cnext
endfor

But I don't know how to get the number of the output of vimgrep.

BTW, I know there have been some plugins, such as EasyGrep, but I still want to make a new one.

Answer 1

Simpler is

function! CustomReplace(target, newWord)
  call CustomGrep(a:target)
  cdo execute 's/'.a:target.'/'.a:newWord.'/gc'
endfunction

Or with cfdo and %s,

function! CustomReplace(target, newWord)
  call CustomGrep(a:target)
  cfdo execute '%s/'.a:target.'/'.a:newWord.'/gc'
endfunction

Answer 2

With the help of @ChristianBrabandt, I finished this function:

function! CustomReplace(target, newWord)
    call CustomGrep(a:target)
    let x = 0
    let cnt = len(getqflist())
    while x < cnt
        execute 's/'.a:target.'/'.a:newWord.'/gc'
        w
        if x != cnt - 1
            cnext
        endif
        let x = x + 1
    endwhile
endfunction

Using getqflist() to get the number to control the loop, that's it.