c语言通过标准库 errno.h 获取错误信息

errno.h 是c语言的一个标准库用来，定义的有个变量errno ,如果程序运行的时候出现了错误，就会对 errno进行赋值， errno 为 0 表示没有错误。

#include <stdio.h>
#include <errno.h>
#include <math.h>

int main() {
    double d = sqrt(100);
    printf("d = %f\t ; errno = %d\n", d, errno);
    d = sqrt(-100);
    printf("d = %f\t ; errno = %d\n", d, errno);
    return 0;
}

输出的结果

d = 10.000000    ; errno = 0
d = -nan         ; errno = 33

这里输出的错误代码是 33, 可以在头文件中看到定义

define EDOM 33 /* Math argument out of domain of function. */

数学函数的参数超出的范围。

strerror 可以输出具体的错误

#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <math.h>

int main() {

    double d = sqrt(100);
    printf("d = %f\t ; errno = %d\n", d, errno);
    d = sqrt(-100);
    printf("d = %f\t ; errno = %d\n", d, errno);
    printf("Error: %s\n", strerror(errno));

    return 0;
}

输出的结果

d = 10.000000    ; errno = 0
d = -nan         ; errno = 33
Error: Numerical argument out of domain

linux中errno的定义文件

"/usr/include/errno.h"
"/usr/include/bits/errno.h"
"/usr/include/linux/errno.h"
"/usr/include/asm/errno.h"

摘选的部分 error的定义

#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  /* Argument 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 */