Lowlevel C Returns Error
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C - Basic Syntax C - Data Types C - Variables C - Constants C - Storage Classes C - Operators C - Decision Making C
C Error Function
- Loops C - Functions C - Scope Rules C - Arrays C c error codes - Pointers C - Strings C - Structures C - Unions C - Bit Fields C - Typedef C
Error Handling In C++
- Input & Output C - File I/O C - Preprocessors C - Header Files C - Type Casting C - Error Handling C - Recursion C - Variable Arguments C fprintf stderr c - Memory Management C - Command Line Arguments C Programming Resources C - Questions & Answers C - Quick Guide C - Useful Resources C - Discussion Selected Reading Developer's Best Practices Questions and Answers Effective Resume Writing HR Interview Questions Computer Glossary Who is Who C - Error Handling Advertisements Previous Page Next Page As such, C programming does not provide direct c error handling best practices support for error handling but being a system programming language, it provides you access at lower level in the form of return values. Most of the C or even Unix function calls return -1 or NULL in case of any error and set an error code errno. It is set as a global variable and indicates an error occurred during any function call. You can find various error codes defined in
the operation. Since EOF is used to report both end of file and random errors, it’s often better to use the feof function to check explicitly for end of file and ferror to check for errors. These functions check
C Stderr
indicators that are part of the internal state of the stream object, indicators set if stderr in c example the appropriate condition was detected by a previous I/O operation on that stream. Macro: int EOF This macro is an integer value
Types Of Errors In C Programming
that is returned by a number of narrow stream functions to indicate an end-of-file condition, or some other error situation. With the GNU C Library, EOF is -1. In other libraries, its value may be some other https://www.tutorialspoint.com/cprogramming/c_error_handling.htm negative number. This symbol is declared in stdio.h. Macro: int WEOF This macro is an integer value that is returned by a number of wide stream functions to indicate an end-of-file condition, or some other error situation. With the GNU C Library, WEOF is -1. In other libraries, its value may be some other negative number. This symbol is declared in wchar.h. Function: int feof (FILE *stream) Preliminary: | MT-Safe | AS-Safe | AC-Unsafe https://www.gnu.org/s/libc/manual/html_node/EOF-and-Errors.html lock | See POSIX Safety Concepts. The feof function returns nonzero if and only if the end-of-file indicator for the stream stream is set. This symbol is declared in stdio.h. Function: int feof_unlocked (FILE *stream) Preliminary: | MT-Safe | AS-Safe | AC-Safe | See POSIX Safety Concepts. The feof_unlocked function is equivalent to the feof function except that it does not implicitly lock the stream. This function is a GNU extension. This symbol is declared in stdio.h. Function: int ferror (FILE *stream) Preliminary: | MT-Safe | AS-Safe | AC-Unsafe lock | See POSIX Safety Concepts. The ferror function returns nonzero if and only if the error indicator for the stream stream is set, indicating that an error has occurred on a previous operation on the stream. This symbol is declared in stdio.h. Function: int ferror_unlocked (FILE *stream) Preliminary: | MT-Safe | AS-Safe | AC-Safe | See POSIX Safety Concepts. The ferror_unlocked function is equivalent to the ferror function except that it does not implicitly lock the stream. This function is a GNU extension. This symbol is declared in stdio.h. In addition to setting the error indicator associated with the stream, the functions that operate on streams also set errno in the same way as the corresponding low-level functions that operate on file descriptors. For example, all of the functions
here for a quick overview of the site Help Center Detailed answers to any questions you might have Meta Discuss the workings and policies of this site About Us Learn more http://stackoverflow.com/questions/19674186/low-level-i-o-read-creat-write-c about Stack Overflow the company Business Learn more about hiring developers or posting ads https://www.chemie.fu-berlin.de/chemnet/use/info/libc/libc_8.html with us Stack Overflow Questions Jobs Documentation Tags Users Badges Ask Question x Dismiss Join the Stack Overflow Community Stack Overflow is a community of 6.2 million programmers, just like you, helping each other. Join them; it only takes a minute: Sign up Low Level I/O - Read/Creat/Write (C) up vote 0 down vote favorite c error I'm trying to use low level functions in C and wanting to read from the STDIN and store that information in a file. int dash, c; char buffer[1024]; if((dash = creat("file.txt", S_IRWXU)) < 0) perror("creat error"); while ((c = read(STDIN_FILENO, buffer, sizeof(buffer))) > 0) { if (write(dash, buffer, c) != c) perror("write error"); I having a problem understanding how I can access 'file.txt' to read it to either print lowlevel c returns to the screen or store to another file. Would I just use 'read("file.txt", buffer, sizeof[buffer])'? EDIT Now after creating "file.txt" I want to open another file, lets say file1 (argv[3]) and dump "file.txt" into file1 (agrv[3]). Would this work? fd = open(argv[3], O_RDWR); //open 3rd arg for writing fd_2 = open("file.txt", O_RDWR); //open created file do { n = read(fd_2, buffer, sizeof(buffer)); if (n < 0) perror("read error argv[2]"); //greater 0=succesful write(STDOUT_FILENO, buffer, n); // this is where I'm stuck } while (n == sizeof(buffer)); close(fd); I have both files open now but can't figure out how to write "file.txt" into argv[3]. c low-level-io share|improve this question edited Oct 30 '13 at 5:17 asked Oct 30 '13 at 4:57 MBan 4814 If you use creat(), you zap the previous content of the file; it is empty. There's nothing to read. –Jonathan Leffler Oct 30 '13 at 5:17 But what if it's the first time "file.txt" is being written into, I should still be able to read from it to copy its contents to another file right? –MBan Oct 30 '13 at 5:23 If the file is created, it is empty. You can, of course, copy the zero bytes t
the higher-level I/O functions described in section Input/Output on Streams, as well as functions for performing low-level control operations for which there are no equivalents on streams. Stream-level I/O is more flexible and usually more convenient; therefore, programmers generally use the descriptor-level functions only when necessary. These are some of the usual reasons: For reading binary files in large chunks. For reading an entire file into core before parsing it. To perform operations other than data transfer, which can only be done with a descriptor. (You can use fileno to get the descriptor corresponding to a stream.) To pass descriptors to a child process. (The child can create its own stream to use a descriptor that it inherits, but cannot inherit a stream directly.) Opening and Closing Files This section describes the primitives for opening and closing files using file descriptors. The open and creat functions are declared in the header file `fcntl.h', while close is declared in `unistd.h'. Function: int open (const char *filename, int flags[, mode_t mode]) The open function creates and returns a new file descriptor for the file named by filename. Initially, the file position indicator for the file is at the beginning of the file. The argument mode is used only when a file is created, but it doesn't hurt to supply the argument in any case.
The flags argument controls how the file is to be opened. This is a bit mask; you create the value by the bitwise OR of the appropriate parameters (using the `|' operator in C). See section File Status Flags, for the parameters available. The normal return value from open is a non-negative integer file descriptor. In the case of an error, a value of -1 is returned instead. In addition to the usual file name syntax errors (see section File Name Errors), the following errno error conditions are defined for this function: EACCES The file exists but is not readable/writable as requested by the flags argument. EEXIST Both O_CREAT and O_EXCL are set, and the named file already exists. EINTR The open operat