《C标准库》阅读笔记

<assert.h>的断言函数适合于用来调试，实际产品中难以使用。

#define NDEBUG 可禁用断言。

#undef NDEBUG 可打开断言。

我自己写的一个例子：

#include <stdio.h>
#define NDEBUG
#include <assert.h>
int main()
{
    ;
    assert(i);
    printf("I am here.");

    ;
}

如果不禁用断言，会输出：test_assert: test_assert.c:7: main: Assertion `i' failed.

Aborted (core dumped)

 

 

宏和函数的区别：

使用宏效率更高，预处理阶段直接替换

调用函数和从函数返回需要更多的时间

---

宏的参数可以出现类型，但是函数不可以

---

使用宏时，宏代码都会被插入程序中，代码长度增加

函数只出现在一个地方，每次使用函数时都调用同一份代码

---

宏参数求值时是在所有周围表达式的上下文环境中，由于操作符的优先级有可能造成不可预测的结果

函数只在被调用时求值一次，更容易预测

 

 

<ctype.h>中声明的函数可以对字符进行判断和转换。

自己写的学习代码：

#include <ctype.h>
#include <stdio.h>

int main()
{
        printf("Input a char,I check its type!\n");
        char c;
        )
        {
                c = getchar();
                if (isalnum(c))
                        printf("isalnum \n");
                if (isalpha(c))
                        printf("isalpha \n");
                if (iscntrl(c))
                        printf("iscntrl \n");
                if (isdigit(c))
                        printf("isdigit \n");
                if (isgraph(c))
                        printf("isgraph \n");
                if (islower(c))
                        printf("islower \n");
                if (isprint(c))
                        printf("isprint \n");
                if (ispunct(c))
                        printf("ispunct \n");
                if (isspace(c))
                        printf("isspace \n");
                if (isupper(c))
                        printf("isupper \n");
                if (isxdigit(c))
                        printf("isxdigit \n");
        }
        ;
} 

errno.h

其实就是错误码。

以下来自linux 2.4.20-18的内核代码中的/usr/include/asm/errno.h

#ifndef _I386_ERRNO_H

#define _I386_ERRNO_H

#define EPERM 1 /* Operation not permitted */

#define ENOENT 2 /* No such file or directory */

#define ESRCH 3 /* No such process */

#define EINTR 4 /* Interrupted system call */

#define EIO 5 /* I/O error */

#define ENXIO 6 /* No such device or address */

#define E2BIG 7 /* Arg list too long */

#define ENOEXEC 8 /* Exec format error */

#define EBADF 9 /* Bad file number */

#define ECHILD 10 /* No child processes */

#define EAGAIN 11 /* Try again */

#define ENOMEM 12 /* Out of memory */

#define EACCES 13 /* Permission denied */

#define EFAULT 14 /* Bad address */

#define ENOTBLK 15 /* Block device required */

#define EBUSY 16 /* Device or resource busy */

#define EEXIST 17 /* File exists */

#define EXDEV 18 /* Cross-device link */

#define ENODEV 19 /* No such device */

#define ENOTDIR 20 /* Not a directory */

#define EISDIR 21 /* Is a directory */

#define EINVAL 22 /* Invalid argument */

#define ENFILE 23 /* File table overflow */

#define EMFILE 24 /* Too many open files */

#define ENOTTY 25 /* Not a typewriter */

#define ETXTBSY 26 /* Text file busy */

#define EFBIG 27 /* File too large */

#define ENOSPC 28 /* No space left on device */

#define ESPIPE 29 /* Illegal seek */

#define EROFS 30 /* Read-only file system */

#define EMLINK 31 /* Too many links */

#define EPIPE 32 /* Broken pipe */

#define EDOM 33 /* Math argument out of domain of func */

#define ERANGE 34 /* Math result not representable */

#define EDEADLK 35 /* Resource deadlock would occur */

#define ENAMETOOLONG 36 /* File name too long */

#define ENOLCK 37 /* No record locks available */

#define ENOSYS 38 /* Function not implemented */

#define ENOTEMPTY 39 /* Directory not empty */

#define ELOOP 40 /* Too many symbolic links encountered */

#define EWOULDBLOCK EAGAIN /* Operation would block */

#define ENOMSG 42 /* No message of desired type */

#define EIDRM 43 /* Identifier removed */

#define ECHRNG 44 /* Channel number out of range */

#define EL2NSYNC 45 /* Level 2 not synchronized */

#define EL3HLT 46 /* Level 3 halted */

#define EL3RST 47 /* Level 3 reset */

#define ELNRNG 48 /* Link number out of range */

#define EUNATCH 49 /* Protocol driver not attached */

#define ENOCSI 50 /* No CSI structure available */

#define EL2HLT 51 /* Level 2 halted */

#define EBADE 52 /* Invalid exchange */

#define EBADR 53 /* Invalid request descriptor */

#define EXFULL 54 /* Exchange full */

#define ENOANO 55 /* No anode */

#define EBADRQC 56 /* Invalid request code */

#define EBADSLT 57 /* Invalid slot */

#define EDEADLOCK EDEADLK

#define EBFONT 59 /* Bad font file format */

#define ENOSTR 60 /* Device not a stream */

#define ENODATA 61 /* No data available */

#define ETIME 62 /* Timer expired */

#define ENOSR 63 /* Out of streams resources */

#define ENONET 64 /* Machine is not on the network */

#define ENOPKG 65 /* Package not installed */

#define EREMOTE 66 /* Object is remote */

#define ENOLINK 67 /* Link has been severed */

#define EADV 68 /* Advertise error */

#define ESRMNT 69 /* Srmount error */

#define ECOMM 70 /* Communication error on send */

#define EPROTO 71 /* Protocol error */

#define EMULTIHOP 72 /* Multihop attempted */

#define EDOTDOT 73 /* RFS specific error */

#define EBADMSG 74 /* Not a data message */

#define EOVERFLOW 75 /* Value too large for defined data type */

#define ENOTUNIQ 76 /* Name not unique on network */

#define EBADFD 77 /* File descriptor in bad state */

#define EREMCHG 78 /* Remote address changed */

#define ELIBACC 79 /* Can not access a needed shared library */

#define ELIBBAD 80 /* Accessing a corrupted shared library */

#define ELIBSCN 81 /* .lib section in a.out corrupted */

#define ELIBMAX 82 /* Attempting to link in too many shared libraries */

#define ELIBEXEC 83 /* Cannot exec a shared library directly */

#define EILSEQ 84 /* Illegal byte sequence */

#define ERESTART 85 /* Interrupted system call should be restarted */

#define ESTRPIPE 86 /* Streams pipe error */

#define EUSERS 87 /* Too many users */

#define ENOTSOCK 88 /* Socket operation on non-socket */

#define EDESTADDRREQ 89 /* Destination address required */

#define EMSGSIZE 90 /* Message too long */

#define EPROTOTYPE 91 /* Protocol wrong type for socket */

#define ENOPROTOOPT 92 /* Protocol not available */

#define EPROTONOSUPPORT 93 /* Protocol not supported */

#define ESOCKTNOSUPPORT 94 /* Socket type not supported */

#define EOPNOTSUPP 95 /* Operation not supported on transport endpoint */

#define EPFNOSUPPORT 96 /* Protocol family not supported */

#define EAFNOSUPPORT 97 /* Address family not supported by protocol */

#define EADDRINUSE 98 /* Address already in use */

#define EADDRNOTAVAIL 99 /* Cannot assign requested address */

#define ENETDOWN 100 /* Network is down */

#define ENETUNREACH 101 /* Network is unreachable */

#define ENETRESET 102 /* Network dropped connection because of reset */

#define ECONNABORTED 103 /* Software caused connection abort */

#define ECONNRESET 104 /* Connection reset by peer */

#define ENOBUFS 105 /* No buffer space available */

#define EISCONN 106 /* Transport endpoint is already connected */

#define ENOTCONN 107 /* Transport endpoint is not connected */

#define ESHUTDOWN 108 /* Cannot send after transport endpoint shutdown */

#define ETOOMANYREFS 109 /* Too many references: cannot splice */

#define ETIMEDOUT 110 /* Connection timed out */

#define ECONNREFUSED 111 /* Connection refused */

#define EHOSTDOWN 112 /* Host is down */

#define EHOSTUNREACH 113 /* No route to host */

#define EALREADY 114 /* Operation already in progress */

#define EINPROGRESS 115 /* Operation now in progress */

#define ESTALE 116 /* Stale NFS file handle */

#define EUCLEAN 117 /* Structure needs cleaning */

#define ENOTNAM 118 /* Not a XENIX named type file */

#define ENAVAIL 119 /* No XENIX semaphores available */

#define EISNAM 120 /* Is a named type file */

#define EREMOTEIO 121 /* Remote I/O error */

#define EDQUOT 122 /* Quota exceeded */

#define ENOMEDIUM 123 /* No medium found */

#define EMEDIUMTYPE 124 /* Wrong medium type */

#endif