如何使用 C++ Inja html template 模板

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C++ html template

Inja是现代C ++的模板引擎，受到jinja for python的启发。它有一个简单而强大的模板语法，包含所有变量，循环，条件，包含，回调，您需要的注释，嵌套和组合，如您所愿。Inja使用nlohmann 的精彩json库进行数据输入和处理。最重要的是，inja只需要两个头文件，这几乎与C ++中的集成一样简单。

下载地址：https://github.com/pantor/inja

教程

模板渲染

使用 json 对象渲染 std::string 字符串模板

json data; data["name"] = "world";render("Hello {{ name }}!", data); // Returns std::string "Hello world!" render_to(std::cout, "Hello {{ name }}!", data); // Prints "Hello world!"

使用环境对象读取本地模板进行渲染

Environment env;// Render a string with json data std::string result = env.render("Hello {{ name }}!", data); // "Hello world!"// Or directly read a template file Template temp = env.parse_template("./templates/greeting.txt"); std::string result = env.render(temp, data); // "Hello world!"data["name"] = "Inja"; std::string result = env.render(temp, data); // "Hello Inja!"// Or read the template file (and/or the json file) directly from the environment result = env.render_file("./templates/greeting.txt", data); result = env.render_file_with_json_file("./templates/greeting.txt", "./data.json");// Or write a rendered template file env.write(temp, data, "./result.txt"); env.write_with_json_file("./templates/greeting.txt", "./data.json", "./result.txt");

可以根据您的需要配置环境类

// With default settings Environment env_default;// With global path to template files and where files will be saved Environment env_1 {"../path/templates/"};// With separate input and output path Environment env_2 {"../path/templates/", "../path/results/"};// Choose between dot notation (like Jinja2) and JSON pointer to access elements env.set_element_notation(ElementNotation::Dot); // (default) e.g. time.start env.set_element_notation(ElementNotation::Pointer); // e.g. time/start// With other opening and closing strings (here the defaults) env.set_expression("{{", "}}"); // Expressions env.set_comment("{#", "#}"); // Comments env.set_statement("{%", "%}"); // Statements {% %} for many things, see below env.set_line_statement("##"); // Line statements ## (just an opener)

变量

变量在 {{...}} 表达式中呈现。

json data; data["neighbour"] = "Peter"; data["guests"] = {"Jeff", "Tom", "Patrick"}; data["time"]["start"] = 16; data["time"]["end"] = 22;// Indexing in array render("{{ guests.1 }}", data); // "Tom"// Objects render("{{ time.start }} to {{ time.end }}pm", data); // "16 to 22pm"

声明

可以使用 {％...％} 语法或整个行的##语法编写语句。

最重要的语句是循环，条件和文件包含。

所有语句都可以嵌套。

循环

// Combining loops and line statements render(R"(Guest List: ## for guest in guests {{ loop.index1 }}: {{ guest }} ## endfor )", data)/* Guest List: 1: Jeff 2: Tom 3: Patrick */

在循环中，定义了特殊变量loop / index（number），loop / index1（number），loop / is_first（boolean）和loop / is_last（boolean）。

在嵌套循环中，父循环变量是可用的，例如，通过 loop/parent/index 。您还可以迭代{％for key，value in time％}等对象。

条件

条件语句支持 if、else if、else 语句。

// Standard comparisons with variable render("{% if time.hour >= 18 %}…{% endif %}", data); // True// Variable in list render("{% if neighbour in guests %}…{% endif %}", data); // True// Logical operations render("{% if guest_count < 5 and all_tired %}…{% endif %}", data); // True// Negations render("{% if not guest_count %}…{% endif %}", data); // True

嵌套

你可以包含其他模板文件或已解析的模板。

// Other template files are included relative from the current file location render({% include "footer.html" %}, data);// To include in-memory templates, add them to the environment first env.include_template("footer", temp); render({% include "footer" %}, data);

函数

在实现 inja 模板语法的过程中，我们实现了一些内置常用函数。

// Upper and lower function, for string cases render("Hello {{ upper(neighbour) }}!", data); // "Hello PETER!" render("Hello {{ lower(neighbour) }}!", data); // "Hello peter!"// Range function, useful for loops render("{% for i in range(4) %}{{ loop.index1 }}{% endfor %}", data); // "1234" render("{% for i in range(3) %}{{ at(guests, i) }} {% endfor %}", data); // "Jeff Tom Patrick "// Length function (please don't combine with range, use list directly...) render("I count {{ length(guests) }} guests.", data); // "I count 3 guests."// Get first and last element in a list render("{{ first(guests) }} was first.", data); // "Jeff was first." render("{{ last(guests) }} was last.", data); // "Patir was last."// Sort a list render("{{ sort([3,2,1]) }}", data); // "[1,2,3]" render("{{ sort(guests) }}", data); // "[\"Jeff\", \"Patrick\", \"Tom\"]"// Round numbers to a given precision render("{{ round(3.1415, 0) }}", data); // 3 render("{{ round(3.1415, 3) }}", data); // 3.142// Check if a value is odd, even or divisible by a number render("{{ odd(42) }}", data); // false render("{{ even(42) }}", data); // true render("{{ divisibleBy(42, 7) }}", data); // true// Maximum and minimum values from a list render("{{ max([1, 2, 3]) }}", data); // 3 render("{{ min([-2.4, -1.2, 4.5]) }}", data); // -2.4// Convert strings to numbers render("{{ int(\"2\") == 2 }}", data); // true render("{{ float(\"1.8\") > 2 }}", data); // false// Set default values if variables are not defined render("Hello {{ default(neighbour, \"my friend\") }}!", data); // "Hello Peter!" render("Hello {{ default(colleague, \"my friend\") }}!", data); // "Hello my friend!"// Check if a key exists in an object render("{{ exists(\"guests\") }}", data); // "true" render("{{ exists(\"city\") }}", data); // "false" render("{{ existsIn(time, \"start\") }}", data); // "true" render("{{ existsIn(time, neighbour) }}", data); // "false"// Check if a key is a specific type render("{{ isString(neighbour) }}", data); // "true" render("{{ isArray(guests) }}", data); // "true" // Implemented type checks: isArray, isBoolean, isFloat, isInteger, isNumber, isObject, isString,

回调函数

您可以使用回调创建自己的更复杂的函数。

函数定义如下：

函数名称
参数数量
函数实现

Environment env;/* * Callbacks are defined by its: * - name * - number of arguments * - callback function. Implemented with std::function, you can for example use lambdas. */ env.add_callback("double", 1, [](Arguments& args) { int number = args.at(0)->get<int>(); // Adapt the index and type of the argument return 2 * number; });// You can then use a callback like a regular function env.render("{{ double(16) }}", data); // "32"// A callback without argument can be used like a dynamic variable: std::string greet = "Hello"; env.add_callback("double-greetings", 0, [greet](Arguments args) { return greet + " " + greet + "!"; }); env.render("{{ double-greetings }}", data); // "Hello Hello!"