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# Manifest Mode: CMake Example
We would like to add [vcpkg manifest support](../users/manifests.md) to an existing cmake project!
Let's create a simple project that prints the fibonacci sequence up to a certain number,
using some common dependencies.
## Initial Layout
Let's create the following file layout:
```no-highlight
fibo/
src/
main.cxx
CMakeLists.txt
```
And we wish to use [fmt](https://github.com/fmtlib/fmt), [range-v3](https://github.com/ericniebler/range-v3),
and [cxxopts](https://github.com/jarro2783/cxxopts).
Let's write our `CMakeLists.txt` first:
```cmake
cmake_minimum_required(VERSION 3.15)
project(fibo CXX)
find_package(fmt REQUIRED)
find_package(range-v3 REQUIRED)
find_package(cxxopts REQUIRED)
add_executable(fibo src/main.cxx)
target_compile_features(fibo PRIVATE cxx_std_17)
target_link_libraries(fibo
PRIVATE
fmt::fmt
range-v3::range-v3
cxxopts::cxxopts)
```
And then we should add `main.cxx`:
```cxx
#include <cxxopts.hpp>
#include <fmt/format.h>
#include <range/v3/view.hpp>
namespace view = ranges::views;
int fib(int x) {
int a = 0, b = 1;
for (int it : view::repeat(0) | view::take(x)) {
(void)it;
int tmp = a;
a += b;
b = tmp;
}
return a;
}
int main(int argc, char** argv) {
cxxopts::Options options("fibo", "Print the fibonacci sequence up to a value 'n'");
options.add_options()
("n,value", "The value to print to", cxxopts::value<int>()->default_value("10"));
auto result = options.parse(argc, argv);
auto n = result["value"].as<int>();
for (int x : view::iota(1) | view::take(n)) {
fmt::print("fib({}) = {}\n", x, fib(x));
}
}
```
This is a simple project of course, but it should give us a clean project to start with.
Let's try it out!
Let's assume you have `fmt`, `range-v3`, and `cxxopts` installed with vcpkg classic mode;
then, you can just do a simple:
```cmd
D:\src\fibo> cmake -B build -S . -DCMAKE_TOOLCHAIN_FILE=D:\src\vcpkg\scripts\buildsystems\vcpkg.cmake
-- Building for: Visual Studio 16 2019
-- Selecting Windows SDK version 10.0.18362.0 to target Windows 10.0.19041.
-- The CXX compiler identification is MSVC 19.27.29111.0
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: C:/Program Files (x86)/Microsoft Visual Studio/2019/Community/VC/Tools/MSVC/14.27.29110/bin/Hostx64/x64/cl.exe - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Configuring done
-- Generating done
-- Build files have been written to: D:/src/fibo/build
D:\src\fibo> cmake --build build
Microsoft (R) Build Engine version 16.7.0+b89cb5fde for .NET Framework
Copyright (C) Microsoft Corporation. All rights reserved.
Checking Build System
Building Custom Rule D:/src/fibo/CMakeLists.txt
main.cxx
The contents of <span> are available only with C++20 or later.
fibo.vcxproj -> D:\src\fibo\build\Debug\fibo.exe
Building Custom Rule D:/src/fibo/CMakeLists.txt
```
And now we can try out the `fibo` binary!
```cmd
D:\src\fibo> .\build\Debug\fibo.exe -n 7
fib(1) = 1
fib(2) = 1
fib(3) = 2
fib(4) = 3
fib(5) = 5
fib(6) = 8
fib(7) = 13
```
it works!
## Converting to Manifest Mode
We now wish to use manifest mode, so all of our dependencies are managed for us! Let's write a `vcpkg.json`:
```json
{
"name": "fibo",
"version-string": "0.1.0",
"dependencies": [
"cxxopts",
"fmt",
"range-v3"
]
}
```
Let's delete the build directory and rerun the build:
```cmd
D:\src\fibo> rmdir /S /Q build
D:\src\fibo> cmake -B build -S . -DCMAKE_TOOLCHAIN_FILE=D:\src\vcpkg\scripts\buildsystems\vcpkg.cmake
-- Running vcpkg install
Detecting compiler hash for triplet x64-windows...
The following packages will be built and installed:
cxxopts[core]:x64-windows
fmt[core]:x64-windows
range-v3[core]:x64-windows
Starting package 1/3: cxxopts:x64-windows
Building package cxxopts[core]:x64-windows...
Using cached binary package: C:\Users\me\AppData\Local\vcpkg/archives\d2\d2d1e5302cdfefef2fd090d8eda84cc0c1fbe6f1.zip
Building package cxxopts[core]:x64-windows... done
Installing package cxxopts[core]:x64-windows...
Installing package cxxopts[core]:x64-windows... done
Elapsed time for package cxxopts:x64-windows: 50.64 ms
Starting package 2/3: fmt:x64-windows
Building package fmt[core]:x64-windows...
Using cached binary package: C:\Users\me\AppData\Local\vcpkg/archives\bf\bf00d5214e912d71414b545b241f54ef87fdf6e5.zip
Building package fmt[core]:x64-windows... done
Installing package fmt[core]:x64-windows...
Installing package fmt[core]:x64-windows... done
Elapsed time for package fmt:x64-windows: 225 ms
Starting package 3/3: range-v3:x64-windows
Building package range-v3[core]:x64-windows...
Using cached binary package: C:\Users\me\AppData\Local\vcpkg/archives\fe\fe2cdedef6953bf954e8ddca471bf3cc8d9b06d7.zip
Building package range-v3[core]:x64-windows... done
Installing package range-v3[core]:x64-windows...
Installing package range-v3[core]:x64-windows... done
Elapsed time for package range-v3:x64-windows: 1.466 s
Total elapsed time: 1.742 s
-- Running vcpkg install - done
-- Selecting Windows SDK version 10.0.18362.0 to target Windows 10.0.19041.
-- The CXX compiler identification is MSVC 19.27.29111.0
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: C:/Program Files (x86)/Microsoft Visual Studio/2019/Community/VC/Tools/MSVC/14.27.29110/bin/Hostx64/x64/cl.exe - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Configuring done
-- Generating done
-- Build files have been written to: D:/src/fibo/build
D:\src\fibo> cmake --build build
Microsoft (R) Build Engine version 16.7.0+b89cb5fde for .NET Framework
Copyright (C) Microsoft Corporation. All rights reserved.
Checking Build System
Building Custom Rule D:/src/fibo/CMakeLists.txt
main.cxx
The contents of <span> are available only with C++20 or later.
fibo.vcxproj -> D:\src\fibo\build\Debug\fibo.exe
Building Custom Rule D:/src/fibo/CMakeLists.txt
```
You can see that with just a _single file_, we've changed over to manifests without _any_ trouble.
The build system doesn't change _at all_! We just add a `vcpkg.json` file, delete the build directory,
and reconfigure. And we're done!
|
