字符串流

std::ostringstream oss;
oss << "CPU: " << 62.5 << "%";      // 格式化拼接
std::string result = oss.str();     // "CPU: 62.5%"

std::istringstream iss("42 3.14 hello");
int a; double b; std::string c;
iss >> a >> b >> c;                 // 解析：42, 3.14, "hello"

#include <iostream>
#include <sstream>
#include <string>
#include <vector>
#include <iomanip>

struct LogEntry {
    std::string timestamp;
    std::string level;
    std::string source;
    std::string message;
    double cpuUsage = 0;
};

LogEntry parseLog(const std::string& line) {
    LogEntry entry;
    std::istringstream iss(line);

    // 格式: "2026-06-14|WARN|web-01|CPU 62.5%|high load"
    std::getline(iss, entry.timestamp, '|');
    std::getline(iss, entry.level, '|');
    std::getline(iss, entry.source, '|');
    std::getline(iss, entry.message, '|');

    // 从 message 中提取数值
    std::istringstream msgStream(entry.message);
    std::string label;
    msgStream >> label >> entry.cpuUsage;  // "CPU 62.5%" → label="CPU", cpuUsage=62.5

    return entry;
}

int main() {
    std::vector<std::string> rawLogs = {
        "2026-06-14 09:00|INFO|web-01|CPU 12.5%|正常",
        "2026-06-14 09:05|WARN|db-02|CPU 62.5%|负载偏高",
        "2026-06-14 09:10|ERROR|cache-03|CPU 95.0%|即将过载",
        "2026-06-14 09:15|INFO|web-02|CPU 8.0%|正常",
        "2026-06-14 09:20|WARN|mq-01|CPU 78.0%|需关注",
    };

    std::cout << "=== 飞翔科技日志解析 ===\n\n";

    // 格式化表头
    std::ostringstream header;
    header << std::left
           << std::setw(22) << "时间"
           << std::setw(8)  << "级别"
           << std::setw(12) << "来源"
           << std::setw(10) << "CPU"
           << "状态";
    std::cout << header.str() << "\n";
    std::cout << std::string(60, '-') << "\n";

    // 解析并输出
    double totalCpu = 0;
    int warnCount = 0;
    for (const auto& raw : rawLogs) {
        auto entry = parseLog(raw);

        std::ostringstream row;
        row << std::left
            << std::setw(22) << entry.timestamp
            << std::setw(8)  << entry.level
            << std::setw(12) << entry.source
            << std::setw(10) << (std::to_string(entry.cpuUsage) + "%")
            << entry.message;
        std::cout << row.str() << "\n";

        totalCpu += entry.cpuUsage;
        if (entry.level == "WARN" || entry.level == "ERROR") ++warnCount;
    }

    std::cout << std::string(60, '-') << "\n";

    // 汇总行
    std::ostringstream summary;
    summary << "平均 CPU: " << std::fixed << std::setprecision(1)
            << (totalCpu / rawLogs.size()) << "%"
            << "  |  告警数: " << warnCount << "/" << rawLogs.size();
    std::cout << summary.str() << "\n";
}

#include <iostream>
#include <sstream>
#include <string>
#include <map>

std::string fillTemplate(const std::string& tpl,
                         const std::map<std::string, std::string>& vars) {
    std::istringstream iss(tpl);
    std::ostringstream oss;
    std::string line;

    while (std::getline(iss, line)) {
        for (const auto& [key, val] : vars) {
            std::string placeholder = "{{" + key + "}}";
            size_t pos;
            while ((pos = line.find(placeholder)) != std::string::npos)
                line.replace(pos, placeholder.length(), val);
        }
        oss << line << "\n";
    }
    return oss.str();
}

int main() {
    std::string tpl = R"(
========================================
  飞翔科技系统通知
========================================

致 {{name}}（{{dept}}部）：

  您的 {{item}} 审核已通过。
  有效期至：{{expireDate}}
  经办人：{{operator}}

如有疑问，请联系技术部（分机 {{ext}}）。

         飞翔科技运维中心
         2026-06-14
)";

    std::map<std::string, std::string> vars = {
        {"name",   "黄俪"},
        {"dept",   "技术"},
        {"item",   "生产环境部署权限"},
        {"expireDate", "2026-12-31"},
        {"operator",   "白歌"},
        {"ext",    "8080"},
    };

    std::string result = fillTemplate(tpl, vars);
    std::cout << result;
}

std::ostringstream oss;
oss << "hello";
oss.str("");  // ✅ 清空内容
oss.clear();  // ✅ 清空状态位（通常也需要）

// ❌ 仅 oss.str("") 不清状态位，可能在错误后仍无法写入

std::ostringstream oss;
oss << "abc";
auto s1 = oss.str();  // "abc"
// oss.str("");        // 清空后重新使用
oss << "def";
auto s2 = oss.str();  // "abcdef"（不是 "def"！需要先 str("") 清空）

std::istringstream iss("1 2 3");
int x;
while (iss >> x) { /* ... */ }
// iss 处于 eofbit 状态
// iss.str("4 5 6");  // 不会自动清除状态位！
iss.clear();           // ✅ 必须
iss.str("4 5 6");