I use OpenCL on an ATI card with the printf extension enabled. I've written a function to print out variables:
void printVar(constant char* name, float var)
{
printf("%s: %f\r\n", name, var);
}
This code works as expected when compiled as plain C, but if i invoke it in OpenCL with
printVar("foo", 0.123);
the result is always some random char followed by 0.123 instead of "foo: 0.123". I guess the compiler has problems with recognizing the char* string, is there a workaround or a fix so i can get the function working?
As I mentioned in my comment I also get the same behavior, however I can suggest a simple workaround for the use case you showed, I.e. when the string is known at compile time we could just use a define statement instead:
#define PRINTVAR(N,X) (printf(N ": %f\r\n", X))
Related
I created a special console log function macro. It works successfully except when there's a comma in the parameter, even if it's part of another expression, i.e. not another argument. I think it's due to the fact that macros are expanded at the pre-processing stage, so the semantic analysis hasn't occurred yet to understand that the comma is not another argument. Here is what I mean:
#define FANCY_LOG(message) [MyLogger logDebug:message withClassAndMethodName: __PRETTY_FUNCTION__ lineNumber: __LINE__];
+(BOOL)logDebug:(NSString *)message withClassAndMethodName:(const char *)name lineNumber:(int)lineNumber;
These work:
FANCY_LOG(#"Hello world");
FANCY_LOG([NSString stringWithFormat:#"Hello!"]);
This does not work:
FANCY_LOG([NSString stringWithFormat:#"Hello %#!", planet]);
Although the comma obviously is part of the NSString expression, the macro interprets it as another argument, I get the following error:
Too many arguments provided to function-like macro invocation
Here's what I have tried unsuccessfully (and variants of these):
#define FANCY_LOG(...) [MyLogger logDebug:##__VA_ARGS___ withClassAndMethodName: __PRETTY_FUNCTION__ lineNumber: __LINE__];
#define FANCY_LOG(message) [MyLogger logDebug:#message withClassAndMethodName: __PRETTY_FUNCTION__ lineNumber: __LINE__];
You are doing that wrong. First of all there are lots of great ready solutions so you do not have reinvent the wheel (don't remember for sure but I think CocoaLumberjack is best).
And your logger can look like this (I've got rusty with Objective C):
+(void) function:(char *)methodName
inLine:(int)line
logs:(NSString *)format, ...;
...
#define FANCY_LOG(...) [MyLogger function: __PRETTY_FUNCTION__ \
inLine: __LINE__ \
logs: __VA_ARGS__]
// then usage:
FANCY_LOG(#"Hello %#!", planet);
First of all I don't know why "g++ -std=c++0x -Wall" would give me warning: invalid suffix on literal; C++11 requires a space between literal and string macro [-Wliteral-suffix] on the following program:
#include <iostream>
#define BEGIN "<b>"
#define END "</b>"
#pragma GCC diagnostic ignored "-Wliteral-suffix"
int main()
{
std::cout << "hello " BEGIN"world"END "\n";
}
Second, I followed gcc doc to ignore "-Wliteral-suffix" but still got the warning. How do I suppress the warning? And why does the compiler warn in the first place?
Ok, to summarize: the failure to suppress the warning is a known gcc bug (gcc.gnu.org/bugzilla/show_bug.cgi?id=61653). Since you cannot (and really, should not) suppress the warning, the easiest fix is to put a space between the literal and the #define string. You can safely do this; it won't change the output text.
The reason this is no longer allowed is because characters directly after a literal string are treated as user-defined literals, which is a new feature in C++11. User-defined literals are considered to be part of the same single token as the literal they modify, thus END will not be subject to replacement by the earlier #define.
I didn't think this was possible but apparently in Objective C it is allowed:
int a = b ?: c;
So you see what they're doing here, they're leaving out the second part of the ternary expression, such that if b is nonzero, b is used as the second part.
It's clever but as far as I know this is against K&R C, and probably ANSI C.
If not, I've been missing out of a terribly clever syntax trick for years...alas!
Update:
It is gcc.
From http://en.wikipedia.org/wiki/%3F%3A
A GNU extension to C allows omitting the second operand, and using implicitly the first operand as the second also:
a = x ? : y;
The expression is equivalent to
a = x ? x : y;
except that if x is an expression, it is evaluated only once. The difference is significant if evaluating the expression has side effects.
This behaviour is defined for both gcc and clang. If you're building macOS or iOS code, there's no reason not to use it.
I would not use it in portable code, though, without carefully considering it.
$ cat > foo.c
#include <stdio.h>
int main(int argc, char **argv)
{
int b = 2;
int c = 4;
int a = b ?: c;
printf("a: %d\n", a);
return 0;
}
$ gcc -pedantic -Wall foo.c
foo.c: In function ‘main’:
foo.c:7: warning: ISO C forbids omitting the middle term of a ?: expression
So no, it's not allowed. What gcc emits in this case does this:
$ ./a.out
a: 2
So the undefined behaviour is doing what you say in your question, even though you don't want to rely on that.
This is a GNU C extension. Check you compiler settings (look for C flavor). Not sure if it's part of Clang, the only information I could get is in this page:
Introduction
This document describes the language extensions provided by Clang. In addition to the language extensions listed here, Clang aims to support a broad range of GCC extensions. Please see the GCC manual for more information on these extensions.
"strnset" is standard-c, (visual c++) and should work in objective-c.
But it doesn't recognize it.
What library am I missing? I have tried: stdio.h and string.h... both don't do it.
what would work in its place where I am given a char array and I want to create: n * characters to be placed in it?
example: _strnset(data, '8', 12); will yield -> data = "888888888888"
Use memset() instead. strnset is not part of the standard "C" library.
What property does strset have over memset that you are interested in?
NAME
memset -- fill a byte string with a byte value
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <string.h>
void *
memset(void *b, int c, size_t len);
DESCRIPTION
The memset() function writes len bytes of value c (converted to an
unsigned char) to the byte string b.
RETURN VALUES
The memset() function returns its first argument.
strnset is actually not a standard C function. It's not present in the GCC headers.
What are the arguments passed into the main method of a command-line program:
int main(int argc, const char * argv[])
what is the first int mean?
And what is the 2nd parameter, is that an array of chars?
How would one use these?
Also, what practical use is a command-line project type, other than using it to learn obj-c i.e. to practise.
argc means "argument count". It signifies how many arguments are being passed into the executable.
argv means "argument values". It is a pointer to an array of characters. Or to think about it in another way, it is an array of C strings (since C strings are just arrays of characters).
So if you have a program "foo" and execute it like this:
foo -bar baz -theAnswer 42
Then in your main() function, argc will be 5, and argv will be:
argv[0] = "/full/path/to/foo";
argv[1] = "-bar";
argv[2] = "baz";
argv[3] = "-theAnswer";
argv[4] = "42";
The parameters to main() are a unix convention for accessing the arguments given on the command line when your program is executed. In a Cocoa app, you can access them the plain old C way, or you can use NSProcessInfo's -arguments method to get them in an NSArray of NSString objects, or use NSUserDefaults to get them as values in a dictionary.
Just to add to the other answers - Objective-C targets both OS X and iOS. And while there is not much value in iOS command line applications, the shell on OS X is still widely used and there are lot of people writing command line tools.
That main is from C and not specific to objective-c. Argc gives you the number of command line arguments passed to your C program. Argv is an array of C strings and contains the command line arguments.
You would use them and the command-line project any time you wanted to write a command line tool or a program you interact with from the command line.
As wikipedia (and any other source says):
int main(void)
int main(int argc, char *argv[])
The parameters argc, argument count, and argv, argument vector, respectively give the number and value of the program's command-line arguments. The names of argc and argv may be any valid identifier in C, but it is common convention to use these names. In C++, the names are to be taken literally, and the "void" in the parameter list is to be omitted, if strict conformance is desired. Other platform-dependent formats are also allowed by the C and C++ standards, except that in C++ the return type must stay int; for example, Unix (though not POSIX.1) and Microsoft Windows have a third argument giving the program's environment, otherwise accessible through getenv in stdlib.h:
int main(int argc, char **argv, char **envp)
Also, what practical use is a command-line project type, other than using it to learn obj-c i.e. to practise.
The practical use is creating a command-line tool using code from a Framework or Application that you have written. Helpers, utilities, launch agents and daemons, all of these background processes are typically implemented as command-line tools.