【cmake系列使用教程】
這個系列的文章翻譯自官方cmake教程：cmake tutorial。
示例程式地址：github.com/rangaofei/t…
不會僅僅停留在官方教程。本人作為一個安卓開發者，實在是沒有linux c程式開發經驗，望大佬們海涵。教程是在macos下完成，大部分linux我也測試過，有特殊說明的我會標註出來。本教程基於cmake-3.10.2，同時認為你已經安裝好cmake。
有時候我們的檔案不是一開始就編寫好的，而是通過在編譯過程中來生成檔案比如某個日誌，構建時間等，等檔案生成後我們需要將這個檔案再新增到應用程式的構建過程中。
下邊，我們將建立一個預先計算的平方根表作為構建過程的一部分，程式可以通過查詢這個表來輸出對應的數值，然後將該表編譯到我們的應用程式中。為了實現這一點，我們首先需要一個生成該表的程式。在mathfunction子目錄中，新建一個檔案，名稱為MakeTable.cxx，內容如下：
// A simple program that builds a sqrt table
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
int main (int argc, char *argv[])
{
int i;
double result;
// make sure we have enough arguments
if (argc < 2)
{
return 1;
}
// open the output file
FILE *fout = fopen(argv[1],"w");
if (!fout)
{
return 1;
}
// create a source file with a table of square roots
fprintf(fout,"double sqrtTable[] = {\n");
for (i = 0; i < 10; ++i)
{
result = sqrt(static_cast<double>(i));
fprintf(fout,"%g,\n",result);
}
// close the table with a zero
fprintf(fout,"0};\n");
fclose(fout);
return 0;
}
複製程式碼注意，該表是作為有效的c++程式碼生成的，輸出的檔名稱是以引數形式傳入的。下一步是將合適的命令新增到mathfunction的CMakeLists.txt檔案中來構建MakeTable的可執行檔案，然後將其作為構建過程的一部分執行。新增如下命令：
# first we add the executable that generates the table
add_executable(MakeTable MakeTable.cxx)
# add the command to generate the source code
add_custom_command (
OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/Table.h
COMMAND MakeTable ${CMAKE_CURRENT_BINARY_DIR}/Table.h
DEPENDS MakeTable
)
# add the binary tree directory to the search path for
# include files
include_directories( ${CMAKE_CURRENT_BINARY_DIR} )
# add the main library
add_library(MathFunctions mysqrt.cxx ${CMAKE_CURRENT_BINARY_DIR}/Table.h )
複製程式碼首先，add_executable(MakeTable MakeTable.cxx)新增了MakeTable這個可執行檔案。然後我們新增一個自定義命令來指定通過執行MakeTable來生成平方根表(Table.h)，注意add_custom_command的第二個引數COMMAND,相當於執行MakeTable並傳入引數${CMAKE_CURRENT_BINARY_DIR}/Table.h。接下來我們要讓CMake知道mysqrt.cxx依賴於生成的檔案表(Table.h)。這是通過新增生成的Table.h檔案到MathFunctions庫來實現的。我們還必須將當前的二進位制目錄新增到包含目錄的列表中，因為生成的表在二進位制目錄中，這樣庫就可以找到幷包含在mysqrt.cxx中。當這個專案被構建時，它將首先構建MakeTable可執行檔案。然後它將執行MakeTable命令生成Table.h檔案。最後，它將編譯mysqrt.cxx和table.h生成mathfunction庫。
根目錄下的的CMakeLists.txt檔案如下:
cmake_minimum_required (VERSION 2.6)
project (Tutorial)
include(CTest)
# The version number.
set (Tutorial_VERSION_MAJOR 1)
set (Tutorial_VERSION_MINOR 0)
# does this system provide the log and exp functions?
include (${CMAKE_ROOT}/Modules/CheckFunctionExists.cmake)
check_function_exists (log HAVE_LOG)
check_function_exists (exp HAVE_EXP)
# should we use our own math functions
option(USE_MYMATH
"Use tutorial provided math implementation" ON)
# configure a header file to pass some of the CMake settings
# to the source code
configure_file (
"${PROJECT_SOURCE_DIR}/TutorialConfig.h.in"
"${PROJECT_BINARY_DIR}/TutorialConfig.h"
)
# add the binary tree to the search path for include files
# so that we will find TutorialConfig.h
include_directories ("${PROJECT_BINARY_DIR}")
# add the MathFunctions library?
if (USE_MYMATH)
include_directories ("${PROJECT_SOURCE_DIR}/MathFunctions")
add_subdirectory (MathFunctions)
set (EXTRA_LIBS ${EXTRA_LIBS} MathFunctions)
endif (USE_MYMATH)
# add the executable
add_executable (Tutorial tutorial.cxx)
target_link_libraries (Tutorial ${EXTRA_LIBS})
# add the install targets
install (TARGETS Tutorial DESTINATION bin)
install (FILES "${PROJECT_BINARY_DIR}/TutorialConfig.h"
DESTINATION include)
# does the application run
add_test (TutorialRuns Tutorial 25)
# does the usage message work?
add_test (TutorialUsage Tutorial)
set_tests_properties (TutorialUsage
PROPERTIES
PASS_REGULAR_EXPRESSION "Usage:.*number"
)
#define a macro to simplify adding tests
macro (do_test arg result)
add_test (TutorialComp${arg} Tutorial ${arg})
set_tests_properties (TutorialComp${arg}
PROPERTIES PASS_REGULAR_EXPRESSION ${result}
)
endmacro (do_test)
# do a bunch of result based tests
do_test (4 "4 is 2")
do_test (9 "9 is 3")
do_test (5 "5 is 2.236")
do_test (7 "7 is 2.645")
do_test (25 "25 is 5")
do_test (-25 "-25 is 0")
do_test (0.0001 "0.0001 is 0.01")
複製程式碼TutorialConfig.h.in檔案如下：
// the configured options and settings for Tutorial
#define Tutorial_VERSION_MAJOR @Tutorial_VERSION_MAJOR@
#define Tutorial_VERSION_MINOR @Tutorial_VERSION_MINOR@
#cmakedefine USE_MYMATH
// does the platform provide exp and log functions?
#cmakedefine HAVE_LOG
#cmakedefine HAVE_EXP
複製程式碼MathFunction資料夾下的CMakeLists.txt檔案內容如下:
# first we add the executable that generates the table
add_executable(MakeTable MakeTable.cxx)
# add the command to generate the source code
add_custom_command (
OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/Table.h
DEPENDS MakeTable
COMMAND MakeTable ${CMAKE_CURRENT_BINARY_DIR}/Table.h
)
# add the binary tree directory to the search path
# for include files
include_directories( ${CMAKE_CURRENT_BINARY_DIR} )
# add the main library
add_library(MathFunctions mysqrt.cxx ${CMAKE_CURRENT_BINARY_DIR}/Table.h)
install (TARGETS MathFunctions DESTINATION bin)
install (FILES MathFunctions.h DESTINATION include)
複製程式碼完整的檔案結構
~/Desktop/Tutorial/Step5/ tree -L 2
.
├── CMakeLists.txt
├── MathFunctions
│ ├── CMakeLists.txt
│ ├── MakeTable.cxx
│ ├── MathFunctions.h
│ └── mysqrt.cxx
├── TutorialConfig.h.in
├── build
└── tutorial.cxx
複製程式碼然後執行外部構建命令(第六個教程裡有說明如何外部構建)：
mkdir build
cd build
cmake ..
make
複製程式碼構建成功後，我們預期會在二進位制資料夾中的MathFunction中生成一個Table.h檔案，並且檔案內容是一個簡單的平方根表。
來看一下結果：
~/Desktop/Tutorial/Step5/ tree -L 3 -I CMakeFiles
.
├── CMakeLists.txt
├── c
│ ├── CMakeLists.txt
│ ├── MakeTable.cxx
│ ├── MathFunctions.h
│ └── mysqrt.cxx
├── TutorialConfig.h.in
├── build
│ ├── CMakeCache.txt
│ ├── CTestTestfile.cmake
│ ├── Makefile
│ ├── MathFunctions
│ │ ├── MakeTable
│ │ ├── Makefile
│ │ ├── Table.h
│ │ ├── cmake_install.cmake
│ │ └── libMathFunctions.a
│ ├── Tutorial
│ ├── TutorialConfig.h
│ └── cmake_install.cmake
└── tutorial.cxx
複製程式碼可以看到，確實有這個表。 然後看一下表的內容是不是0-9的平方根且最後以0結束，執行命令：
~/Desktop/Tutorial/Step5/ cat build/MathFunctions/Table.h
double sqrtTable[] = {
0,
1,
1.41421,
1.73205,
2,
2.23607,
2.44949,
2.64575,
2.82843,
3,
0};
複製程式碼結果正確。這種構建方式增加了蛋疼的操作，獲取用python指令碼或者shell指令碼更容易生成，但是為了展示cmake系統構建的強大功能，一次編寫到處執行，我們忍一忍吧。