Section 6: introduction to cmake grammar

cmake

• cmake It's an open source build tool .cmake Is the solution Makefile Many kinds , Different specifications .cmake It's a cross platform building tool . yes Makefile It's the top tool of the game . Automatically build makefile, Instead of developers building manually makefile The tedious process of .
• At present, many open source projects have CMakeLists.txt file , Fast implementation of cross platform construction source code . Truly accomplish "Write Once,Run everywhere".

CMake Variable

1. cmake The file includes commands + notes + Space + Line break ;
2. cmake Write the source file with CMakeLists.txt or .cmake For extended
3. CMakeLists.txt Write the construction rules of the whole project ( Put the directory at the top ), It can be done by add_subdirectory() The command adds the construction rules of the next level source directory
4. Cmake All valid statements in the source file of China are commands

Common variable names

1. PROJECT_NAME project The project name written in the command
2. CMAKE_VERSION Currently in use cmake edition
3. CMAKE_SOURCE_DIR Project top level directory , machine CMakeLists File path
4. PROJECT_SOURCE_DIR Same as CMAKE_SOURCE_DIR
5. CMAKE_BINARY_DIR The directory where the project compilation takes place , The perform cmake Command the directory for project configuration , It's usually build
6. CMAKE_CURRENT_SOURCE_DIR At present CMakeLists.txt Path
7. CMAKE_CURRRENT_BINARY_DIR What is being processed CMakeLists.txt The compilation directory where the target file is generated in
8. CMAKE_CURRENT_LIST_FILE: The output calls the variable CMakeLists.txt The full path to the file

notes

use “#” Annotate , From the beginning to the end of the line ;

Variable

1. grammar : set( Variable name A variable's value )
   1. Be careful : Variable names are case sensitive

set(var 711) #  Define variable values 
message("var = ${var}")
message("PATH = $ENV{PATH}")  #  environment variable 

bool Variable

• Boolean variable size sensitivity

true：1, ON, YES, TRUE, Y,  Not 0 Value 
false：0, OFF, NO, FALSE, N, IGNORE, NOTFOUND,  An empty string ””,  With -NOTFOUND  a null-terminated string 

• example

set(true 1)
set(false OFF)
message("true = " ${true})
message("false = " ${false})

list

• If a variable has multiple values , An unquoted quotation cmake Will automatically split into multiple list elements at the semicolon , And pass them to the command as multiple independent parameters . Quoted quotation cmake Don't slice and keep semicolon still , The entire quotation mark is passed to the command as a parameter .

set(list_var 1 2 3 4) # list_var = 1;2;3;4
set(list_foo "5;6;7;8") # list_foo = 5;6;7;8
message(${list_var})# Output ： 1234
message(${list_foo})# Output ：5678
message("${list_var}")# Output ：1;2;3;4
message("${list_foo}")# Output ：5;6;7;8

cmake command

stay cmake in , Conditional statements , Loop statement , Function or macro , It's all orders .

The operator

Operator priority ： One yuan > binary > Logic

 Logic 
NOT, AND, OR

 One yuan 
EXISTS, COMMAND, DEFINED.

 binary 
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

Conditional commands

if( expression )
  #  Command block to execute 
  COMMAND1(ARGS ...)
  COMMAND2(ARGS ...)
elseif( expression 2)
  #  Command block to execute 
  COMMAND1(ARGS ...)
  COMMAND2(ARGS ...)
else( expression )
  #  Command block to execute 
  COMMAND1(ARGS ...)
  COMMAND2(ARGS ...)
endif( expression )

Circular command

1. The loop can be used break() Command exit ,continue() The command can skip the following statement block , Immediately enter the next cycle iteration .

while( expression )
  #  Command block to execute 
  COMMAND1(ARGS ...)
  COMMAND2(ARGS ...)
  # break  Exit loop 
  # continue  Exit the current cycle , So let's move on to the next cycle 
endwhile( expression )

Traverse

1. foreach Also support break(),continue() The command operation .

foreach( Loop variable   Parameters 1  Parameters 2 ...)
  #  Command block to execute 
  COMMAND1(ARGS ...)
  COMMAND2(ARGS ...)
endforeach( Loop variable )

Custom command ( function )

The command can take string parameters , But no return value . Command names are case insensitive , therefore SET and set Indicates the same command , But the parameter names in the command are case sensitive ARG and arg Are two different parameters .

# Custom function command format ：
function(<name> [arg1 [arg2 [arg3 ...]]])
#  Custom command block 
  COMMAND1(ARGS ...)
  COMMAND2(ARGS ...)
endfunction(<name>)

# call 
name( [arg1 [arg2 [arg3 ...]]])

Custom macro commands

1. Macros and functions are basically the same , Just say that function commands have their own scope , The scope of the macro command is the same as that of the caller .

macro(<name> [arg1 [arg2 [arg3 ...]]])
  COMMAND1(ARGS ...)
  COMMAND2(ARGS ...)
endmacro(<name>)

Scope

1. Cmake Three scopes : Global layer / Directory layer / Function layer .
2. Global layer : cache Variable , Visible throughout the project , Generally in use set When defining a variable, specify CACHE Parameters can be defined as cache The variable of .
3. Directory layer ： In the current directory CMakeLists.txt In the definition of , And included in this document （ adopt include perhaps macro Imported ） Other cmake The variables defined in the source file belong to the scope of the directory layer .
4. Function layer ： Variables defined in the command function , Variables within the scope of a function .
5. Global layer < Directory layer < Function layer , Variables with small scope of action will cover variables with large scope of action .
6. The variables of the upper scope are modified in the current scope , It will not be passed to the scope of the upper layer （ The current scope is just copying all variables of the previous scope to its own scope for modification ）, For example, modify a variable defined by the directory layer scope in the function command , It does not affect the value of this variable in the directory layer .
7. If the modification passes set The command explicitly specifies PARENT_SCOPE Parameters , The modified variable scope is in the upper scope , Instead of the current scope .