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This program crashes before it even runs!
This program crashes before it even runs! (When single-stepping with a debugger, it dies before the first statement in main.) You probably have one or more very large (kilobyte or more) local arrays. Many systems have fixed-size stacks, and even those which perform dynamic stack allocation automatic... 2015-05-29, 1535👍, 0💬

How can f be used for both float and double arguments in printf? Aren't they different types?
How can f be used for both float and double arguments in printf? Aren't they different types? In the variable-length part of a variable-length argument list, the ``default argument promotions'' apply: types char and short int are promoted to int, and float is promoted to double. (These are the same ... 2015-06-17, 1534👍, 0💬

How can I suppress the dreaded MS-DOS Abort, Retry, Ignore? message?
How can I suppress the dreaded MS-DOS Abort, Retry, Ignore? message? Among other things, you need to intercept the DOS Critical Error Interrupt, interrupt 24H. See the comp.os.msdos.programmer 2015-04-06, 1534👍, 0💬

How do I read the arrow keys? What about function keys?
How do I read the arrow keys? What about function keys? Terminfo, some versions of termcap, and some versions of curses have support for these non-ASCII keys. Typically, a special key sends a multicharacter sequence (usually beginning with ESC, '\033'); parsing these can be tricky. (curses will do t... 2015-04-24, 1532👍, 0💬

How can I call a function with an argument list built up at run time?
How can I call a function with an argument list built up at run time? There is no guaranteed or portable way to do this. Instead of an actual argument list, you might consider passing an array of generic (void *) pointers. The called function can then step through the array, much like main() might s... 2015-06-03, 1530👍, 0💬

How can I invoke another program or command and trap its output?
How can I invoke another program or command and trap its output? Unix and some other systems provide a popen function, which sets up a stdio stream on a pipe connected to the process running a command, so that the calling program can read the output (or alternatively supply the input). Using popen, ... 2015-03-16, 1530👍, 0💬

I have an old macro that doesn't seem to work any more....
I have an old macro #define CTRL(c) ('c' &amp; 037) that doesn't seem to work any more. The intended use of this macro is in code like tchars.t_eofc = CTRL(D); which is expected to expand to tchars.t_eofc = ('D' &amp; 037); based on the assumption that the actual value of the parameter c wil... 2016-01-25, 1528👍, 0💬

I thought that using large model meant that I could use more than 64K of data!
What does the error message ``DGROUP data allocation exceeds 64K'' mean, and what can I do about it? I thought that using large model meant that I could use more than 64K of data! Even in large memory models, MS-DOS compilers apparently toss certain data (strings, some initialized global or static v... 2015-03-20, 1528👍, 0💬

Why is the macro giving me the warning
Why is the macro #define TRACE(n) printf("TRACE: %d\n", n) giving me the warning ``macro replacement within a string literal''? It seems to be expanding TRACE(count); as printf("TRACE: %d\count", count); Some pre-ANSI compilers/preprocessors interpreted macro definitions like #define TRACE(var, fmt)... 2016-01-25, 1526👍, 0💬

How do I copy files?
How do I copy files? Either use system() to invoke your operating system's copy utility, or open the source and destination files (using fopen or some lower-level file-opening system call), read characters or blocks of characters from the source file, and write them to the destination file. Here is ... 2015-04-08, 1526👍, 0💬

How can I read in an object file and jump to locations in it?
How can I read in an object file and jump to locations in it? You want a dynamic linker or loader. It may be possible to malloc some space and read in object files, but you have to know an awful lot about object file formats, relocation, etc., and this approach can't work if code and data reside in ... 2015-03-09, 1525👍, 0💬

How can I increase the allowable number of simultaneously open files?
I'm getting an error, ``Too many open files''. How can I increase the allowable number of simultaneously open files? A: There are typically at least two resource limitations on the number of simultaneously open files: the number of low-level ``file descriptors'' or ``file handles'' available in the ... 2015-04-03, 1524👍, 0💬

How can I find the day of the week given the date?
How can I find the day of the week given the date? Here are three methods: 1. Use mktime or localtime # . Here is a code fragment which computes the day of the week for February 29, 2000: #include &lt;stdio.h> #include &lt;time.h> char *wday[] = {"Sunday", "Monday", "Tuesday", "Wednesday", "... 2015-01-07, 1524👍, 0💬

How can I generate random numbers with a normal or Gaussian distribution?
How can I generate random numbers with a normal or Gaussian distribution? There are a number of ways of doing this. 1. Exploit the Central Limit Theorem (``law of large numbers'') and add up several uniformly-distributed random numbers: #include &lt;stdlib.h> #include &lt;math.h> #define NSU... 2015-07-22, 1523👍, 0💬

How can I ensure that integer arithmetic doesnt overflow?
How can I ensure that integer arithmetic doesnt overflow? The usual approach is to test the operands against the limits in the header file &lt;limits.h> before doing the operation. For example, here is a ``careful'' addition function: int chkadd(int a, int b) { if(INT_MAX - b &lt; a) { fputs... 2015-03-04, 1522👍, 0💬

I have a simple little program that reads characters until EOF ...
I have a simple little program that reads characters until EOF, but how do I actually enter that ``EOF'' value from the keyboard? I see that EOF is defined by to be -1; am I supposed to enter -1? If you think about it, what you enter can't be -1, because ``-1'' is two characters, and getchar is read... 2015-11-16, 1520👍, 0💬

Where can I get an ANSI-compatible lint?
Where can I get an ANSI-compatible lint? Products called PC-Lint and FlexeLint are available from Gimpel Software. The Unix System V release 4 lint is ANSI-compatible, and is available separately (bundled with other C tools) from UNIX Support Labs or from System V resellers. Another ANSI-compatible ... 2015-05-05, 1520👍, 0💬

How can I write data files which can be read on other machines with different word size, byte order, or floating point formats?
How can I write data files which can be read on other machines with different word size, byte order, or floating point formats? The most portable solution is to use text files (usually ASCII), written with fprintf and read with fscanf or the like. (Similar advice also applies to network protocols.) ... 2015-02-23, 1519👍, 0💬

I have a varargs function which accepts a float parameter
I have a varargs function which accepts a float parameter. Why isn't va_arg(argp, float) working? In the variable-length part of variable-length argument lists, the old ``default argument promotions'' apply: arguments of type float are always promoted (widened) to type double, and types char and sho... 2015-06-08, 1518👍, 0💬

I need a sort of an approximate strcmp routine ...
I need a sort of an approximate strcmp routine ... Q: I need a sort of an ``approximate'' strcmp routine, for comparing two strings for close, but not necessarily exact, equality. A:Some nice information and algorithms having to do with approximate string matching, as well as a useful bibliography, ... 2015-01-09, 1518👍, 0💬

Does C have anything like the `substr extract substrin routine present in other languages?
Does C have anything like the `substr extract substrin routine present in other languages? Not as such. To extract a substring of length LEN starting at index POS in a source string, use something like char dest[LEN+1]; strncpy(dest, &source[POS], LEN); dest[LEN] = '\0'; /* ensure \0 termination... 2016-03-07, 1517👍, 0💬

Is exit(status) truly equivalent to returning the same status from main?
Is exit(status) truly equivalent to returning the same status from main? Yes and no. The Standard says that a return from the initial call to main is equivalent to calling exit. However, a return from main cannot be expected to work if data local to main might be needed during cleanup; A few very ol... 2015-03-09, 1517👍, 0💬

I have got this tricky preprocessing I want to do and I cant figure out a way to do it.
I have got this tricky preprocessing I want to do and I cant figure out a way to do it. C's preprocessor is not intended as a general-purpose tool. (Note also that it is not guaranteed to be available as a separate program.) Rather than forcing it to do something inappropriate, you might want to wri... 2016-01-19, 1516👍, 0💬

Why does everyone say not to use gets?
Why does everyone say not to use gets? Unlike fgets(), gets() cannot be told the size of the buffer it's to read into, so it cannot be prevented from overflowing that buffer if an input line is longer than expected--and Murphy's Law says that, sooner or later, a larger-than-expected input line will ... 2015-10-16, 1516👍, 0💬

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.NET C C++ CSS DBA General HTML Java JavaScript JSP JUnit MySQL Networking Oracle Perl Perl PHP PL/SQL RSS Software QA SQL Server Struts Unix Windows XHTML XML