Setting cmake variable in command line and comparing it with string

Question

I'm calling my CMakeLists.txt like this:

cmake ../.. -DTARGET=JETSON_NANO

Then, this line:

message(STATUS "------------ TARGET: ${TARGET}")

prints ------------ TARGET: JETSON_NANO

but this line:

if (TARGET STREQUAL JETSON_NANO)

gives error:

if given arguments: "TARGET" "STREQUAL" "JETSON_NANO"

Why? TARGET is setted!

Note, that when use string literal with STREQUAL or some other if construction, it is better to enclose this literal with double quotes: "JETSON_NANO". Otherwise, if the variable with given name exists, CMake will substitute value of the variable instead of the literal. This is, however, unrelated to your issue. — Tsyvarev
– Tsyvarev, Commented Sep 2, 2019 at 7:51

Tsyvarev · Accepted Answer · 2019-09-02 07:49:16Z

TARGET is a special keyword for if command. It is used for check whether given target (in CMake sense) exists. Correct usage of this keyword includes two arguments of if:

if(TARGET JETSON_NANO) # Checks whether CMake target JETSON_NANO exists

This is why CMake emits error when you use this keyword with three arguments:

if (TARGET STREQUAL "JETSON_NANO") # Error: 'TARGET' keyword requires two `if` arguments

However, you may swap compared strings in if command:

if ("JETSON_NANO" STREQUAL TARGET) # Compares string "JETSON_NANO" with variable TARGET

See more about if command in its documentation.

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