Task that calls another task in tasks.json

Question

I have two tasks build all and C/C++: build in my tasks.json defined below. build all calls C/C++: build. I have launch.json that calls tasks:

{
    "version": "0.2.0",
    "configurations": [
        {
            //...
            //"preLaunchTask": "C/C++: build"
            "preLaunchTask": "build all"
            //...
        }

        ]
}

If task calls C/C++: build, everything goes fine. If task calls build all nothing is happening. Why build all not calls C/C++: build?

tasks.json

{
    // See https://go.microsoft.com/fwlink/?LinkId=733558
    // for the documentation about the tasks.json format
    "version": "2.0.0",
    "tasks": [
        {
            "type": "cppbuild",
            "label": "C/C++: build",
            "command": "/usr/bin/g++",
            "args": [
                "-g",
                "${workspaceFolder}/*.cpp",
                "-o",
                "${fileDirname}/${fileBasenameNoExtension}"
            ],
            "options": {
                "cwd": "${workspaceFolder}"
            },
            "problemMatcher": [
                "$gcc"
            ],
            "group": {
                "kind": "build",
                "isDefault": true
            },
            "detail": "compiler: /usr/bin/g++"
        },
        {
            "label": "build all",
            "dependsOn": [
                "C/C++: build"
            ],
            "group": {
                "kind": "build",
                "isDefault": true
            }
        }


    ]
}