cmake build_error ai_generated true

CMake Error: add_library cannot create target "mylib" because another target with the same name already exists.

ID: cmake/target-already-exists

Also available as: JSON · Markdown · 中文
85%Fix Rate
88%Confidence
1Evidence
2024-03-15First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
cmake 3.22 active — — —
cmake 3.28 active — — —
cmake 3.30 active — — —

Root Cause

A target with the same name is defined twice in the same directory scope, typically due to duplicate add_library or add_executable calls, or a misspelled target name in a subdirectory.

generic

中文

在同一目录范围内重复定义了同名目标，通常是由于重复的 add_library 或 add_executable 调用，或子目录中目标名称拼写错误。

Official Documentation

https://cmake.org/cmake/help/latest/command/add_library.html

Workarounds

  1. 85% success Ensure each target has a unique name across all subdirectories. Use `add_library(mylib STATIC src/mylib.cpp)` only once. If needed, use `set_target_properties` to alias or create an INTERFACE library with a different name. 
    Ensure each target has a unique name across all subdirectories. Use `add_library(mylib STATIC src/mylib.cpp)` only once. If needed, use `set_target_properties` to alias or create an INTERFACE library with a different name.
  2. 95% success If the duplicate is intentional (e.g., from FetchContent), wrap in `if(NOT TARGET mylib)` before definition: if(NOT TARGET mylib) add_library(mylib STATIC src/mylib.cpp) endif() 
    If the duplicate is intentional (e.g., from FetchContent), wrap in `if(NOT TARGET mylib)` before definition:
if(NOT TARGET mylib)
  add_library(mylib STATIC src/mylib.cpp)
endif()

中文步骤

  1. Ensure each target has a unique name across all subdirectories. Use `add_library(mylib STATIC src/mylib.cpp)` only once. If needed, use `set_target_properties` to alias or create an INTERFACE library with a different name.
  2. If the duplicate is intentional (e.g., from FetchContent), wrap in `if(NOT TARGET mylib)` before definition:
if(NOT TARGET mylib)
  add_library(mylib STATIC src/mylib.cpp)
endif()

Dead Ends

Common approaches that don't work:

  1. 60% fail

    The real cause is a duplicate definition; renaming may hide the issue but the original duplicate remains, causing other targets to reference the wrong one.

  2. 90% fail

    The error is in CMakeLists.txt logic, not cached state; clearing cache does not fix duplicate target definitions.

  3. 100% fail

    target_compile_definitions does not create or rename targets; it only adds compile definitions to existing targets.