该头文件引入 C 标准库头文件 errno.h并将相关标识符加入 std 命名空间。目录1 说明1 说明包含该头文件可以保证 C 标准库头文件中具有外部链接的名称会在 std 命名空间中进行声明。语法#includecerrno宏#defineerrno#defineE2BIG#defineEACCES#defineEADDRINUSE#defineEADDRNOTAVAIL#defineEAFNOSUPPORT#defineEAGAIN#defineEALREADY#defineEBADF#defineEBADMSG#defineEBUSY#defineECANCELED#defineECHILD#defineECONNABORTED#defineECONNREFUSED#defineECONNRESET#defineEDEADLK#defineEDESTADDRREQ#defineDEOM#defineEEXIST#defineEFAULT#defineEFBIG#defineEHOSTUNREACH#defineEIDRM#defineEILSEQ#defineEINPROGRESS#defineEINTR#defineEINVAL#defineEIO#defineEISCONN#defineEISDIR#defineELOOP#defineEMFILE#defineEMLINK#defineEMSGSIZE#defineENAMETOOLONG#defineENETDOWN#defineENETRESET#defineENETUNREACH#defineENFILE#defineENOBUFS#defineENODATA#defineENODEV#defineENOENT#defineENOEXEC#defineENOLCK#defineENOLINK#defineENOMEM#defineENOMSG#defineENOPROTOOPT#defineENOSPC#defineENOSR#defineENOSTR#defineENOSYS#defineENOTCONN#defineENOTDIR#defineENOTEMPTY#defineENOTRECOVERABLE#defineENOTSOCK#defineENOTSUP#defineENOTTY#defineENXIO#defineEOPNOTSUPP#defineEOVERFLOW#defineEOWNERDEAD#defineEPERM#defineEPIPE#defineEPROTO#defineEPROTONOSUPPORT#defineEPROTOTYPE#defineERANGE#defineEROFS#defineESPIPE#defineESRCH#defineETIME#defineETIMEDOUT#defineETXTBSY#defineEWOULDBLOCK#defineEXDEV备注这里的全部宏均由POSIX标准所定义使用提示errno用于保存系统调用、库函数出错后的错误码现代实现中它是线程局部变量。应当在函数调用失败后立刻读取后续库函数调用可能覆盖该值。