在老项目工程中使用cocoapods，可能会报这个错误:library not found for -lPods .
导致这个错误可能有两个原因，这两个原因在编译过程中都是有蛛丝马迹可循的。
原因1：
在 pod install时，就会有告警信息提示：
xxx target overrides the `OTHER_LDFLAGS` build setting defined in `Pods/Target Support Files/Pods/Pods.debug.xcconfig'. This can lead to problems with the CocoaPods installation
xxx target overrides the `HEADER_SEARCH_PATHS` build setting defined in `Pods/Target Support Files/Pods/Pods.release.xcconfig'. This can lead to problems with the CocoaPods installation
xxx target overrides the `OTHER_CFLAGS` build setting defined in `Pods/Target Support Files/Pods/Pods.release.xcconfig'. This can lead to problems with the CocoaPods installation
- Use the `$(inherited)` flag, or
- Remove the build settings from the target.
- Use the `$(inherited)` flag, or
- Remove the build settings from the target.
- Use the `$(inherited)` flag, or
- Remove the build settings from the target.
- Use the `$(inherited)` flag, or
- Remove the build settings from the target.
- Use the `$(inherited)` flag, or
- Remove the build settings from the target.
- Use the `$(inherited)` flag, or
- Remove the build settings from the target.
很明确的告知：通过添加 `$(inherited)` flag 可以解决该问题。
根据调试确认，OTHER_LDFLAGS 指的是 other linker flags; OTHER_CFLAGS 指的是 other c flags；HEADER_SEARCH_PATHS 指的是 header search paths.
将这三处修改完毕后再次运行pod install，可以发现告警信息已经不再出现了。
原因2：
在编译时有如下的警告和错误：
1.警告： Target 'Pods' of project 'Pods' was rejected as an implicit dependency for 'libPods.a' because its architectures 'arm64' didn't contain all required architectures 'armv7 arm64'
2.错误： ld: library not found for -lpop
clang: error: linker command failed with exit code 1 (use -v to see invocation)
这里不留神可能警告会被忽略（毕竟在一个老项目中有一些警告很正常），但这个警告才是问题的关键。
pod里面的build选项里build active architecture only 在 debug情形下默认是 YES, 这里如果和你项目的该设置不匹配（笔者用来调试的项目这里设置就是NO）的话那么就会报告该错误。
在pods里面的target中挨个修改其配置和原有的工程一致，然后clean编译，项目即可正常运行。