Error reporting (errno.h)

Include errno.h for the runtime error indicator and numeric error codes.

Variables and Macros

Name	Meaning
errno	Global error indicator for the single-threaded dcc runtime.
EPERM	Operation not permitted.
ENOENT	No such file or directory.
ESRCH	No such process.
EINTR	Interrupted function call.
EIO	Input/output error.
ENXIO	No such device or address.
E2BIG	Argument list too long.
ENOEXEC	Executable file format error.
EBADF	Bad file descriptor.
ECHILD	No child processes.
EAGAIN	Resource temporarily unavailable.
ENOMEM	Not enough memory.
EACCES	Permission denied.
EFAULT	Bad address.
EBUSY	Device or resource busy.
EEXIST	File exists.
EXDEV	Cross-device link.
ENODEV	No such device.
ENOTDIR	Not a directory.
EISDIR	Is a directory.
EINVAL	Invalid argument.
ENFILE	Too many files open in system.
EMFILE	Too many open files.
ENOTTY	Inappropriate I/O control operation.
EFBIG	File too large.
ENOSPC	No space left on device.
ESPIPE	Invalid seek.
EROFS	Read-only file system.
EMLINK	Too many links.
EPIPE	Broken pipe.
EDOM	Domain error.
ERANGE	Result too large or out of range.
ENOTEMPTY	Directory not empty.

Runtime model

The DCC C Compiler runtime is single-threaded, so errno is one global int. Runtime calls set it when they fail; successful calls are not required to clear it. Test the function result first, then inspect errno only on failure.

C89 requires EDOM and ERANGE. DCC C Compiler also defines conventional small-system and POSIX-style file errors used by the CP/M file and directory support.

Error checks

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

FILE *fp = fopen("DATA.TXT", "r");
if (!fp) {
    if (errno == ENOENT)
        puts("missing file");
    else
        printf("open failed: %d\n", errno);
}

Use strerror(errno) from string.h or perror from stdio.h when you want runtime text for an error code.