42

我想要一个简单的教程来告诉我加载一个 yaml 文件并解析数据。Expat 风格会很棒，但任何能够以某种形式实际向我展示数据的解决方案都会很有用。

到目前为止，我在 yaml-0.1.1 源代码中为 C 运行了多个测试，我要么得到一个错误，要么没有输出，要么在 run-emitter.c 的情况下。它读入 yaml 文件并将其打印到 STDOUT，它不会通过 libyaml 函数/结构生成文本。在出现错误的情况下，我不知道是文件错误还是我的构建不正确（我没有修改任何内容......）文件是从 yaml.org 复制的

谁能指点我一个教程？（我用谷歌搜索了至少 30 分钟，阅读了任何看起来相关的内容）或具有良好教程或示例的库的名称。也许您可以告诉我文件中加载了哪些 libyaml 测试并对其进行了处理，或者我为什么会出错。本文档不解释如何使用该文件，只解释如何加载它。

http://pyyaml.org/wiki/LibYAML#Documentation

4

5 回答 5

66

为 C++ 解析器尝试yaml-cpp（如这个问题所建议的）。

披露：我是作者。

示例语法（来自教程）：

YAML::Node config = YAML::LoadFile("config.yaml");

if (config["lastLogin"]) {
  std::cout << "Last logged in: " << config["lastLogin"].as<DateTime>() << "\n";
}

const std::string username = config["username"].as<std::string>();
const std::string password = config["password"].as<std::string>();
login(username, password);
config["lastLogin"] = getCurrentDateTime();

std::ofstream fout("config.yaml");
fout << config;
于 2009-05-08T06:02:10.683 回答
12

C 示例 - 将 YAML 树解析为glib “N-ary 树”：

#include <yaml.h>
#include <stdio.h>
#include <glib.h>

void process_layer(yaml_parser_t *parser, GNode *data);
gboolean dump(GNode *n, gpointer data);



int main (int argc, char **argv) {
    char *file_path = "test.yaml";
    GNode *cfg = g_node_new(file_path);
    yaml_parser_t parser;

    FILE *source = fopen(file_path, "rb");
    yaml_parser_initialize(&parser);
    yaml_parser_set_input_file(&parser, source);
    process_layer(&parser, cfg); // Recursive parsing
    yaml_parser_delete(&parser);
    fclose(source);

    printf("Results iteration:\n");
    g_node_traverse(cfg, G_PRE_ORDER, G_TRAVERSE_ALL, -1, dump, NULL);
    g_node_destroy(cfg);

    return(0);
}



enum storage_flags { VAR, VAL, SEQ }; // "Store as" switch

void process_layer(yaml_parser_t *parser, GNode *data) {
    GNode *last_leaf = data;
    yaml_event_t event;
    int storage = VAR; // mapping cannot start with VAL definition w/o VAR key

    while (1) {
        yaml_parser_parse(parser, &event);

        // Parse value either as a new leaf in the mapping
        //  or as a leaf value (one of them, in case it's a sequence)
        if (event.type == YAML_SCALAR_EVENT) {
            if (storage) g_node_append_data(last_leaf, g_strdup((gchar*) event.data.scalar.value));
            else last_leaf = g_node_append(data, g_node_new(g_strdup((gchar*) event.data.scalar.value)));
            storage ^= VAL; // Flip VAR/VAL switch for the next event
        }

        // Sequence - all the following scalars will be appended to the last_leaf
        else if (event.type == YAML_SEQUENCE_START_EVENT) storage = SEQ;
        else if (event.type == YAML_SEQUENCE_END_EVENT) storage = VAR;

        // depth += 1
        else if (event.type == YAML_MAPPING_START_EVENT) {
            process_layer(parser, last_leaf);
            storage ^= VAL; // Flip VAR/VAL, w/o touching SEQ
        }

        // depth -= 1
        else if (
            event.type == YAML_MAPPING_END_EVENT
            || event.type == YAML_STREAM_END_EVENT
        ) break;

        yaml_event_delete(&event);
    }
}


gboolean dump(GNode *node, gpointer data) {
    int i = g_node_depth(node);
    while (--i) printf(" ");
    printf("%s\n", (char*) node->data);
    return(FALSE);
}
于 2009-03-07T06:57:41.300 回答
11

我在 http://wpsoftware.net/andrew/pages/libyaml.html写了一个教程。

这涵盖了在 C 中使用 libyaml 的基础知识，使用基于令牌和基于事件的解析。它包括用于输出 YAML 文件内容的示例代码。

于 2011-01-12T20:53:45.403 回答
5

“yaml load lang:c++”的谷歌代码搜索（现已失效）将此作为第一个链接：demo.cc：

#include <iyaml++.hh>
#include <tr1/memory>
#include <iostream>
#include <stdexcept>

using namespace std;

// What should libyaml++ do when a YAML entity is parsed?
// NOTE:  if any of the event handlers is not defined, a respective default
// no-op handler will be used.  For example, not defining on_eos() is
// equivalent to defining void on_eos() { }.
class my_handler : public yaml::event_handler {
    void on_string(const std::string& s) { cout << "parsed string:  " << s << endl; }
    void on_integer(const std::string& s) { cout << "parsed integer:  " << s << endl; }
    void on_sequence_begin() { cout << "parsed sequence-begin." << endl; }
    void on_mapping_begin() { cout << "parsed mapping-begin." << endl; }
    void on_sequence_end() { cout << "parsed sequence-end." << endl; }
    void on_mapping_end() { cout << "parsed mapping-end." << endl; }
    void on_document() { cout << "parsed document." << endl; }
    void on_pair() { cout << "parsed pair." << endl; }
    void on_eos() { cout << "parsed eos." << endl; }
};

// ok then, now that i know how to behave on each YAML entity encountered, just
// give me a stream to parse!
int main(int argc, char* argv[])
{
    tr1::shared_ptr<my_handler> handler(new my_handler());
    while( cin ) {
        try { yaml::load(cin, handler); } // throws on syntax error

        catch( const runtime_error& e ) {
            cerr << e.what() << endl;
        }
    }
    return 0;
}
于 2008-12-13T13:50:18.767 回答
3

作为替代品yaml-cpp，libyaml还有rapidyaml。这是一个例子。

#include <fstream>
#include <iostream>
#include <sstream>
#include <string>

#include <ryml_std.hpp>
#include <ryml.hpp>

std::string get_file_contents(const char *filename)
{
    std::ifstream in(filename, std::ios::in | std::ios::binary);
    if (!in) {
        std::cerr << "could not open " << filename << std::endl;
        exit(1);
    }
    std::ostringstream contents;
    contents << in.rdbuf();
    return contents.str();
}

int main(int argc, char const *argv[]) 
{
    std::string contents = get_file_contents("config.yml");
    ryml::Tree tree = ryml::parse(ryml::to_csubstr(contents));
    ryml::NodeRef foo = tree["foo"];
    for (ryml::NodeRef const& child : foo.children()) {
        std::cout << "key: " << child.key() << " val: " << child.val() << std::endl;
    }
    return 0;
}

配置.yaml

foo:
  bar: a
  barbar: b
  barbarbar: c
于 2021-10-13T08:29:11.703 回答