Your requirements could not be resolved to an installable set of packages.

执行composer install遇到错误：Your requirements could not be resolved to an installable set of packages. 这是因为不匹配composer.json要求的版本,错误代码如下。

Loading composer repositories with package information
Installing dependencies (including require-dev) from lock file
Your requirements could not be resolved to an installable set of packages.

  Problem 1
    - Installation request for doctrine/annotations v1.6.0 -> satisfiable by doc                                          trine/annotations[v1.6.0].
    - doctrine/annotations v1.6.0 requires php ^7.1 -> your PHP version (7.0.12)                                           does not satisfy that requirement.
  Problem 2
    - Installation request for doctrine/cache v1.7.1 -> satisfiable by doctrine/                                          cache[v1.7.1].
    - doctrine/cache v1.7.1 requires php ~7.1 -> your PHP version (7.0.12) does                                           not satisfy that requirement.
  Problem 3
    - Installation request for doctrine/collections v1.5.0 -> satisfiable by doc                                          trine/collections[v1.5.0].
    - doctrine/collections v1.5.0 requires php ^7.1 -> your PHP version (7.0.12)                                           does not satisfy that requirement.
  Problem 4
    - Installation request for doctrine/common v2.8.1 -> satisfiable by doctrine                                          /common[v2.8.1].
    - doctrine/common v2.8.1 requires php ~7.1 -> your PHP version (7.0.12) does                                           not satisfy that requirement.
  Problem 5
    - Installation request for doctrine/dbal v2.7.1 -> satisfiable by doctrine/d                                          bal[v2.7.1].
    - doctrine/dbal v2.7.1 requires php ^7.1 -> your PHP version (7.0.12) does n                                          ot satisfy that requirement.
  Problem 6
    - Installation request for doctrine/inflector v1.3.0 -> satisfiable by doctr                                          ine/inflector[v1.3.0].
    - doctrine/inflector v1.3.0 requires php ^7.1 -> your PHP version (7.0.12) d                                          oes not satisfy that requirement.
  Problem 7
    - Installation request for symfony/css-selector v4.1.0 -> satisfiable by sym                                          fony/css-selector[v4.1.0].
    - symfony/css-selector v4.1.0 requires php ^7.1.3 -> your PHP version (7.0.1                                          2) does not satisfy that requirement.
  Problem 8
    - Installation request for symfony/event-dispatcher v4.1.0 -> satisfiable by                                           symfony/event-dispatcher[v4.1.0].
    - symfony/event-dispatcher v4.1.0 requires php ^7.1.3 -> your PHP version (7                                          .0.12) does not satisfy that requirement.
  Problem 9
    - Installation request for symfony/translation v4.1.0 -> satisfiable by symf                                          ony/translation[v4.1.0].
    - symfony/translation v4.1.0 requires php ^7.1.3 -> your PHP version (7.0.12                                          ) does not satisfy that requirement.
  Problem 10
    - Installation request for doctrine/instantiator 1.1.0 -> satisfiable by doc                                          trine/instantiator[1.1.0].
    - doctrine/instantiator 1.1.0 requires php ^7.1 -> your PHP version (7.0.12)                                           does not satisfy that requirement.
  Problem 11
    - Installation request for myclabs/deep-copy 1.8.1 -> satisfiable by myclabs                                          /deep-copy[1.8.1].
    - myclabs/deep-copy 1.8.1 requires php ^7.1 -> your PHP version (7.0.12) doe                                          s not satisfy that requirement.
  Problem 12
    - doctrine/inflector v1.3.0 requires php ^7.1 -> your PHP version (7.0.12) d                                          oes not satisfy that requirement.
    - laravel/framework v5.5.40 requires doctrine/inflector ~1.1 -> satisfiable                                           by doctrine/inflector[v1.3.0].
    - Installation request for laravel/framework v5.5.40 -> satisfiable by larav                                          el/framework[v5.5.40].

查看了下资料说是php版本不符,打开composer.json发现代码只要求大于7.0.0可仍然报这个错误,不用太较真执行如下代码之后在运行之前的代码就ok

composer install --ignore-platform-reqs 或者 composer update --ignore-platform-reqs