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
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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(" << 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 << ",'" << EscapeString(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
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"{} {}".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
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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(fmt_spec.data() + idx, fmt_spec.size() - idx); }
template <typename T, typename... Types> static void BuildFormatString(std::ostringstream& builder, 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
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uint32_t ts = butil::gettimeofday_s(); string sql_formattor = "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, orde |
