更优雅的C++字符串格式化实现方法详解

目录

• 背景
• 优化
• 实现
• 使用

背景

在用C++编写代码时，经常需要用到字符串拼接及格式化，尤其是在拼写sql语句时，目前大部分sql拼接方式都是通过ostringstream流一点一点拼接的，代码可读性很差而且很容易拼接错误

    ostringstream sqlstr;
    sqlstr << "insert into virtual_item_info(id, platform, typeid, name, icon_url, act_url, "
              "desc_text, vm_typeid, vm_price, val_typeid, val_count, priority, show_type, param, "
              "combo, area, "
              "onshelf_time, offshelf_time, status, show_url, svga_url, mp4_url, remarks_info, "
              "shading_url, utime, has_green_dot, act_id, "
              "act_name, act_icon, act_name_lang_id, act_start_time, act_end_time, item_level, "
              "distribute_src, buy_to_use_duration, noble_lvl, name_lang_id, desc_lang_id, "
              "target_whitelist_id, target_whitelist_type, is_cp_shareable, act_link_type, "
              "act_show_type, item_lang_code)"
           << "values(" <android;< item.id << "," << item.platform << "," << item.atypeid << ",'"
           << EscapeString(item.name) << "','" << EscapeString(item.iconurl) << "','"
           << EscapeString(item.actUrl) << "','" << EscapeString(item.desctext) << "',"
           << item.vmtypeid << "," << item.vmprice << "," << item.valtypeid << "," << item.valcount
           << "," << item.priority << "," << item.showType << ",'" << EjsscapeString(item.param)
           << "'," << item.isCombo << ",'" << EscapeString(item.area) << "',"
           << item.onshelftime << "," << item.offshelftime << "," << item.status << ",'"
           << EscapeString(item.showUrl) << "','" << EscapeString(item.svgaUrl) << "','"
           << EscapeString(item.mp4Url) << "','" << EscapeString(item.remarksInfo)
           << "', '" << EscapeString(item.shadingUrl) << "', " << butil::gettimeofday_s()
           << "," << item.hasGreenDot << ",'" << EscapeString(item.actId) << "','"
           << EscapeString(item.actName) << "','" << EscapeString(item.actIcon) << "','"
           << EscapeString(item.actNameLangId) << "'," << item.actStartTime << ","
           << item.actEndTime << "," << item.itemLevel << "," << item.distributeSrc << ","
           << item.buyToUseDuration << "," << item.nobleLevel << ",'"
           << EscapeString(item.nameLangId) << "','" << EscapeString(item.descLangId)
           << "','" << EscapeString(item.targetGroupWhiteListId) << "',"
           << item.targetGroupWhiteListType << "," << item.isCpShareable << "," << item.actLinkType
           << "," << item.actShowType << ",'" << EscapeString(item.itemLangCode) << "')";

优化

参考python字符串格式化方式

"{} {}".format("hello", "world")

先写出完整的字符串，在需要替换的位置通过占位符{}保留， 最后将占位符替换为指定的参数

实现

本质是基于递归依次将字符转中的占位符{}替换为对应的参数

class StringUtil {
private:
    // 递归出口
    static void BuildFormatString(std::ostringstream& builder,
                                  const std::string& fmt_spec,
                                  std::string::size_type idx) {
        builder.write(fmjst_spec.data() + idx, fmt_spec.size() - idx);
    }


    template <typename T, typename... Ty开发者_C开发pes>
    static void BuildFormatString(std::ostringstream& builder,
http://www.devze.com                                  const std::string& fmt_spec,
                                  std::string::size_type idx,
                                  const T& first,
                                  const Types&... args) {
        auto pos = fmt_spec.find_first_of("{}", idx);a
        if (pos == std::string::npos) {
            builder.write(fmt_spec.data() + idx, fmt_spec.size() - idx);
            return;
        }

        builder.write(fmt_spec.data() + idx, pos - idx);
        builder << first;
        BuildFormatString(builder, fmt_spec, pos + 2, args...);
    }

public:
    /**
    * C++实现python风格字符串格式化
    */
    template <typename... Types>
    static std::string FormatString(const std::string& fmt_spec, const Types&... args) {
        std::ostringstream builder;
        BuildFormatString(builder, fmt_spec, 0, args...);
        return builder.str();
    }
};

使用

uint32_t ts = butil::gettimeofday_s();
string sql_formattor =
       javascript "insert into tbl_user_relation_info(uid, gift_id, BATch_id, relation_id, crc32_relation_id, status, peer_uid, relation_create_time, create_time, update_time, order_id) values({}, {}, {}, '', 0, 0, 0, 0, {}, {}, '{}')";
string sql = StringUtil::FormatString(sql_formattor, uid, giftId, batchId, ts, ts, orderId);

到此这篇关于更优雅的C++字符串格式化实现方法详解的文章就介绍到这了,更多相关C++字符串格式化内容请搜索我们以前的文章或继续浏览下面的相关文章希望大家以后多多支持我们！