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
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