如何使用 C++ Inja html template 模板

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!"

注释

可以使用 {＃...＃} 语法编写注释

render("Hello{# Todo #}!", data); // "Hello!"

支持的编译器

Inja使用string_view从C ++ 17，但包括填充工具从martinmoene。这样，最低版本是C ++ 11。目前，以下编译器已经经过测试：

• GCC 5.0 - 8.0
• Clang 5.0 - 6.0
• Microsoft Visual C++ 2015 - 2017