Briefly introduce how to use cmake (3) function

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We have used message to output the information output when cmake compiles before. Let's output the name of the project. The project name is stored in the variable PROJECT_NAME and we ${}can extract the variable value.

message("${PROJECT_NAME}")
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This will output the value of the variable that stores the item name, then ${variable} will extract the value of the variable, if the variable does not exist, this time it will output an empty string.

message("project name = ${PROJECT_NAME}")
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But this is not general enough, we can define the function print to output the variable name.

Next, use the function instruction to define a function, the first parameter is the function name, and the second parameter is the parameter

function(print var)
    message("${var} = ${${var}}")
endfunction()

print(PROJECT_NAME)
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${var}The parsing here is the variable name we passed in, so the first output ${var}output is PROJECT_NAME and then the PROJECT_NAME variable is fetched, so it ${${var}}is

We can also give only the function name without giving the parameter name when defining the function in the function instruction, and then we can obtain one or more parameters of the input function through some built-in variables (parameters).

parameter name	illustrate
ARGN	get parameter list
ARGC	Get the number of parameters
ARGV	get parameter value

PROJECT_NAME;MyVAR
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set(MyVAR "hello world")

function(print)
    message("${ARGN}")
endfunction()

print(PROJECT_NAME MyVAR)

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set(MyVAR "hello world")

function(print)
    message("${ARGN}")
    message("${ARGC}")
    message("${ARGV0}")
endfunction()

print(PROJECT_NAME MyVAR)
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PROJECT_NAME is a cmake own variable and a custom MyVAR with the value "hello world". When defining the function, we did not define any variables as formal parameters, because some built-in variables are provided for functions in cmake so that we can access the user input variables through these variables, so the advantage is that the number of variables is variable. When we pass in two variables.

PROJECT_NAME;MyVAR
2
PROJECT_NAME
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ARGN is a set of variable names, ARGC variable value is the number of input variables, and ARGV holds a list of all arguments given to the function

set(MyVAR "hello world")

function(print)
    message("${ARGN}")
    message("${ARGC}")
    foreach(var ${ARGN})
        message("${ARGV}==${${var}}")    
    endforeach()
endfunction()

print(PROJECT_NAME MyVAR)
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We can use the foreach statement to traverse the ARGN

Briefly introduce how to use cmake (3) function

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