Cmake Use Tutorial (7) – Processes and loops

Cmake (cmake)

Cmake Use tutorial (1) – start

Cmake Tutorial 2 – Adding libraries

Cmake use tutorial (3) – installation, testing, system self – check

Cmake Use tutorial (4) – file generator

Cmake Use tutorial (5) -cpack generate installation package

Cmake Use tutorial (6) – lousy syntax

Cmake Use Tutorial (7) – Processes and loops

Cmake: Macro and Function

This series of articles was translated from the official Cmake tutorial: CMake Tutorial.

Example program address: github.com/rangaofei/t…

It will not stop at the official tutorial. I as an Android developer, is really no Linux C program development experience, hope big guys forgive. The tutorial is done on MacOS, and I’ve tested most Linux as well, so IF there are special instructions, I’ll note them. This tutorial is based on cmake-3.10.2 and assumes that you have cmake installed.

The process to judge

Process judgment in Cmake is relatively simple and close to C language.

The form is as follows:

if(expression)
  # then section.
  COMMAND1(ARGS ...)
  COMMAND2(ARGS ...)
  #...
elseif(expression2)
  # elseif section.
  COMMAND1(ARGS ...)
  COMMAND2(ARGS ...)
  #...
else(expression)
  # else section.
  COMMAND1(ARGS ...)
  COMMAND2(ARGS ...)
  #...
endif(expression)
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One caveat here: Else and Endif expressions can be omitted. At Beth Israel I have to add a SET(CMAKE_ALLOW_LOOSE_LOOP_CONSTRUCTS) to cover all of the expressions. I don’t have an API for that variable. That’s why I don’t even write it.

If expressions can be long, in order of precedence:

> EXISTS, COMMAND, DEFINED 
> EQUAL, LESS, LESS_EQUAL, GREATER, GREATER_EQUAL, STREQUAL, STRLESS, STRLESS_EQUAL, STRGREATER, STRGREATER_EQUAL, VERSION_EQUAL, VERSION_LESS, VERSION_LESS_EQUAL, VERSION_GREATER, VERSION_GREATER_EQUAL, MATCHES
> NOT,AND,OR
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This is a long list, but it doesn’t contain much:

In an if expression, you don’t need to use ${var} to get the value of the variable. For example, set two variables and compare the values:

set(var1 OFF)
set(var2 "var1")
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If (var2) = false; if(var1) = false; If (${var2}) = if(${var1});

The foreach loop

1. First form

foreach(loop_var arg1 arg2 ...) COMMAND1(ARGS ...) COMMAND2(ARGS ...) . endforeach(loop_var)Copy the code

Note here that the variables of endforeach(loop_var) should not be omitted, because foreach loops rely on variables to break out of the loop.

All commands between foreach and matching endforeach are logged and not called. Once endforeach is found, the original logging command is executed. Before each iteration of the loop, ${loop_var} is set to a variable with the current value in the list.

foreach(i 0 1 2 3)
    message(STATUS "current is ${i}")
endforeach(i)
    message(STATUS "end")
endforeach(i)
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A simple loop, but with an extra endforeach. Look at the results

Those who qualify can qualify can qualify onto university. ➜ StepTest git:(master) qualify cmake -p foreach. Cmake -- current is 0 -- current is 1 -- current is 2 -- current is 3 -- end CMake Error at foreach.cmake:5 (endforeach): endforeach An ENDFOREACH command was found outside of a proper FOREACH ENDFOREACH structure. Or its arguments did not match the opening FOREACH command.Copy the code

An error. No matching foreach.

2. The second form

foreach(loop_var RANGE total)
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From 0 to the end of total (including total)

foreach(i RANGE 3)
    message(STATUS "current is ${i}")
endforeach(i)
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The range will be 0-3, check the result:

Those who qualify can qualify can qualify onto university. ➜ StepTest git:(master) qualify cmake -p foreach. Cmake -- current is 0 -- current is 1 -- current is 2 -- current is 3Copy the code

3. The Third form

foreach(loop_var RANGE start stop [step])
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The value from start until the end of stop can be set to step.

foreach(i RANGE 0 3 1)
message(STATUS "current is ${i}")
endforeach(i)
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The output is the same as above.

Note that the final result is not greater than the stop value, and the step value is converted to an integer when it is a float

4. Fourth form

foreach(loop_var IN [LISTS [list1 [...]]]
                    [ITEMS [item1 [...]]])
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Also easier, more LIST keyword to loop LIST. Don’t tell.

The while loop

while(condition) COMMAND1(ARGS ...) COMMAND2(ARGS ...) . endwhile(condition)Copy the code

Note that conditions in endwhile are best left out. This condition is the same rule as the expression in if. The loop takes the form of a foreach loop, executing each instruction until it hits endwhile.

In while and foreach loops, use ${var} to fetch the value of a variable. Use “break” and “continue” in the same way as “c”.

In real projects, option is often used with if. Option is relatively simple to use:

option(<option_variable> "help string describing option"
       [initial value])
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Initial value can only be ON or OFF. If not set, the default value is False. Cmake_dependent_option is a module built into cmake that generates an option dependent on another option. This is a pain in the guts.

Look at a simple example:

include(${CMAKE_ROOT}/Modules/CMakeDependentOption.cmake)
option(USE_CURL "use libcurl" ON)
option(USE_MATH "use libm" ON)
cmake_dependent_option(DEPENT_USE_CURL "this is dependent on USE_CURL" ON "USE_CURL; NOT USE_MATH" OFF)
if(DEPENT_USE_CURL)
    message(STATUS "using lib curl")
else(a)message(STATUS "not using lib curl")
endif(a)Copy the code

The first line contains the dependency modules we need.

The second and third lines define two options: USE_CURL,USE_MATH, ON.

This is dependent on USE_CURL; this is dependent on USE_CURL; this is dependent on USE_CURL; If NOT USE_MATH is true, take the front value, otherwise take the back value.

Lines 5-9 are an if statement that prints the desired result.

Output results:

Those who qualify can qualify can qualify onto university. ➜ StepTest git:(master) qualify cmake -p optionc.cmake -- not using lib curlCopy the code