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Wiki source code of ROS Crash Course

Last modified by Leon Poon on 2021/08/30 23:24
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1 (% class="wikigeneratedid" id="HC2B2BCrashCrashCourse" %)
2 Using C++.
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4 == Day 1 ==
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6 main function
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8 g++ source1.cpp -o program1
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10 Paths, "/" and "." and ".." in navigating directories - absolute vs relative
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12 data type - binary itself is meaningless unless you say what information that the binary bits represent
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14 declare variables (int, char, string as series of chars)
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16 statements end with semicolon
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18 cstdio library #include
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20 calling a function - printf
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22 if condition block else block (example: do something different based on argc)
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24 for loop - 3 statements (initialiser, condition, post-loop advancement) and a code block
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26 Homework: study "while" loop and "switch" statement
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28 == Day 2 ==
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30 While loop - condition and 1 code block.
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32 Do while loop - code block then condition.
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34 While loop = for loop with empty initialiser/advancement statements
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36 Switch - match expression's result to case label, execute statements until break.
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38 Switch vs if-else differences - number of times expressions are evaluated
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40 write your own function
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42 calling with parameters copied as separate set of var values in function
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44 classes as blueprints.
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46 complex var data type - instances of a class all have the same set of fields
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48 the "." field accessor (var1.func1() etc)
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50 each instance have it's own separate memory for storing data.
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52 Example code - fibonacci sequence.
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54 Value overflow because not enough number of bits to represent large numbers.
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56 Various integer data types - specifier in printf
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58 Homework: implement factorial (1 to 20) calculator
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60 in Linux, most things are case-sensitive. (A not equals a)
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62 == Day 3 ==
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64 factorial printer - 2 approaches:
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66 1. for-loop that goes 1 to 20 and each loop calls fact(n ) function and prints return.
67 1. for-loop that goes 1 to 20 and multiplies once each time and print.
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69 set initial values of vars when declaring otherwise initial values are unpredictable
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71 factorial function - implemented in recursive way, closer to mathematical definition
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73 stack memory
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75 stack frame to store var values in each function call
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77 stack overflow/crash (segfault)
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79 base condition to stop the recursion
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81 recursive algorithms are common - e.g. when dealing with trees
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83 spaces in file/directory names and how to navigate - space is special in terminal
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85 understand names chosen by yourself vs names chosen by other people for your use
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87 creating ros package - arguments: package name, dependencies
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89 CMakeLists.txt (.txt file can also be used with other programs)
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91 cmake = build tool - compile many files in some defined ways
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93 package.xml - information for ROS
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95 compiling - carefully read and understand and seek answers to error messages
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97 msg files - fields declaration with data type
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99 create cpp file for a node
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101 quick reading of code for publisher node
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103 homework: implement message subscriber node according to ROS book
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105 == Day 4 ==
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107 message subscriber.
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109 argc and agrv
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111 node name during ros::init
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113 topic advertise/subscribe explained.
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115 subscribe() only memorises that this node wants messages and what to do with them.
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117 subscribe() - providing name of function. not calling.
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119 publisher while ros::ok() loop.
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121 subscriber spin() loop - handle events.
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123 the double-colon operator: (1) namespace (2) static member of class
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125 pointers are memory addresses
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127 arrow -> operator
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129 array are elements in sequence in memory.
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131 char ~*~* = pointer of pointer of char data.
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