C/C++ errno用法

errno是全局变量，表示上一个调用的错误代码，如果成功就为0.

使用示例如下：

#include <iostream>#include <stdio.h>#include <string.h>#include <errno.h>using namespace std;int main(){    FILE *fp;    if ( (fp = fopen("no/such/file","r+")) == NULL )    {        printf("errON[%d]errMsg[%s]\n",errno,strerror(errno));    }}

include errno.h后可直接使用errno，

include string.h后可用strerror(errno)将errno这个整形变量转化为对应的可读的字符串，具体对应关系见 /usr/include/asm/errno.h中定义如下

#defineEPERM 1/* Operation not permitted */#defineENOENT 2/* No such file or directory */#defineESRCH 3/* No such process */#defineEINTR 4/* Interrupted system call */#defineEIO 5/* I/O error */#defineENXIO 6/* No such device or address */#defineE2BIG 7/* Argument list too long */#defineENOEXEC 8/* Exec format error */#defineEBADF 9/* Bad file number */#defineECHILD10/* No child processes */#defineEAGAIN11/* Try again */#defineENOMEM12/* Out of memory */#defineEACCES13/* Permission denied */#defineEFAULT14/* Bad address */#defineENOTBLK15/* Block device required */#defineEBUSY16/* Device or resource busy */#defineEEXIST17/* File exists */#defineEXDEV18/* Cross-device link */#defineENODEV19/* No such device */#defineENOTDIR20/* Not a directory */#defineEISDIR21/* Is a directory */#defineEINVAL22/* Invalid argument */#defineENFILE23/* File table overflow */#defineEMFILE24/* Too many open files */#defineENOTTY25/* Not a typewriter */#defineETXTBSY26/* Text file busy */#defineEFBIG27/* File too large */#defineENOSPC28/* No space left on device */#defineESPIPE29/* Illegal seek */#defineEROFS30/* Read-only file system */#defineEMLINK31/* Too many links */#defineEPIPE32/* Broken pipe */#defineEDOM33/* Math argument out of domain of func */#defineERANGE34/* Math result not representable */<pre name="code" class="cpp">#defineEDEADLK35/* Resource deadlock would occur */#defineENAMETOOLONG36/* File name too long */#defineENOLCK37/* No record locks available */#defineENOSYS38/* Function not implemented */#defineENOTEMPTY39/* Directory not empty */#defineELOOP40/* Too many symbolic links encountered */#defineEWOULDBLOCKEAGAIN/* Operation would block */#defineENOMSG42/* No message of desired type */#defineEIDRM43/* Identifier removed */#defineECHRNG44/* Channel number out of range */#defineEL2NSYNC45/* Level 2 not synchronized */#defineEL3HLT46/* Level 3 halted */#defineEL3RST47/* Level 3 reset */#defineELNRNG48/* Link number out of range */#defineEUNATCH49/* Protocol driver not attached */#defineENOCSI50/* No CSI structure available */#defineEL2HLT51/* Level 2 halted */#defineEBADE52/* Invalid exchange */#defineEBADR53/* Invalid request descriptor */#defineEXFULL54/* Exchange full */#defineENOANO55/* No anode */#defineEBADRQC56/* Invalid request code */#defineEBADSLT57/* Invalid slot */#defineEDEADLOCKEDEADLK#defineEBFONT59/* Bad font file format */#defineENOSTR60/* Device not a stream */#defineENODATA61/* No data available */#defineETIME62/* Timer expired */#defineENOSR63/* Out of streams resources */#defineENONET64/* Machine is not on the network */#defineENOPKG65/* Package not installed */#defineEREMOTE66/* Object is remote */#defineENOLINK67/* Link has been severed */#defineEADV68/* Advertise error */#defineESRMNT69/* Srmount error */#defineECOMM70/* Communication error on send */#defineEPROTO71/* Protocol error */#defineEMULTIHOP72/* Multihop attempted */#defineEDOTDOT73/* RFS specific error */#defineEBADMSG74/* Not a data message */#defineEOVERFLOW75/* Value too large for defined data type */#defineENOTUNIQ76/* Name not unique on network */#defineEBADFD77/* File descriptor in bad state */#defineEREMCHG78/* Remote address changed */#defineELIBACC79/* Can not access a needed shared library */#defineELIBBAD80/* Accessing a corrupted shared library */#defineELIBSCN81/* .lib section in a.out corrupted */#defineELIBMAX82/* Attempting to link in too many shared libraries */#defineELIBEXEC83/* Cannot exec a shared library directly */#defineEILSEQ84/* Illegal byte sequence */#defineERESTART85/* Interrupted system call should be restarted */#defineESTRPIPE86/* Streams pipe error */#defineEUSERS87/* Too many users */#defineENOTSOCK88/* Socket operation on non-socket */#defineEDESTADDRREQ89/* Destination address required */#defineEMSGSIZE90/* Message too long */#defineEPROTOTYPE91/* Protocol wrong type for socket */#defineENOPROTOOPT92/* Protocol not available */#defineEPROTONOSUPPORT93/* Protocol not supported */#defineESOCKTNOSUPPORT94/* Socket type not supported */#defineEOPNOTSUPP95/* Operation not supported on transport endpoint */#defineEPFNOSUPPORT96/* Protocol family not supported */#defineEAFNOSUPPORT97/* Address family not supported by protocol */#defineEADDRINUSE98/* Address already in use */#defineEADDRNOTAVAIL99/* Cannot assign requested address */#defineENETDOWN100/* Network is down */#defineENETUNREACH101/* Network is unreachable */#defineENETRESET102/* Network dropped connection because of reset */#defineECONNABORTED103/* Software caused connection abort */#defineECONNRESET104/* Connection reset by peer */#defineENOBUFS105/* No buffer space available */#defineEISCONN106/* Transport endpoint is already connected */#defineENOTCONN107/* Transport endpoint is not connected */#defineESHUTDOWN108/* Cannot send after transport endpoint shutdown */#defineETOOMANYREFS109/* Too many references: cannot splice */#defineETIMEDOUT110/* Connection timed out */#defineECONNREFUSED111/* Connection refused */#defineEHOSTDOWN112/* Host is down */#defineEHOSTUNREACH113/* No route to host */#defineEALREADY114/* Operation already in progress */#defineEINPROGRESS115/* Operation now in progress */#defineESTALE116/* Stale NFS file handle */#defineEUCLEAN117/* Structure needs cleaning */#defineENOTNAM118/* Not a XENIX named type file */#defineENAVAIL119/* No XENIX semaphores available */#defineEISNAM120/* Is a named type file */#defineEREMOTEIO121/* Remote I/O error */#defineEDQUOT122/* Quota exceeded */#defineENOMEDIUM123/* No medium found */#defineEMEDIUMTYPE124/* Wrong medium type */#defineECANCELED125/* Operation Canceled */#defineENOKEY126/* Required key not available */#defineEKEYEXPIRED127/* Key has expired */#defineEKEYREVOKED128/* Key has been revoked */#defineEKEYREJECTED129/* Key was rejected by service *//* for robust mutexes */#defineEOWNERDEAD130/* Owner died */#defineENOTRECOVERABLE131/* State not recoverable */#define ERFKILL132/* Operation not possible due to RF-kill */

附录(感觉说的不错拷到这里来)：

stdin、stdout、stderr 就是三个文件流指针。分别表示标准输入，输出，错误输出。系统会为每一个进程打开这三个文件

上面三个变量都是一个打开的文件的句柄，stdout，stderr一般关联到终端，stdin一般关联到键盘
如：
FILE *fd;
fd=fopen("file","mode");
stdin、stdout、stderr 就跟fd的用法是一样的。