Today I'm writing this program and I had has two problems.
This is the full code in Objective-C for a OS X Project:
#import <Foundation/Foundation.h>
int main(int argc, const char * argv[])
{
#autoreleasepool {
int numx;
int quadr;
NSLog(#"Inserisci un numero");
scanf("%i", &numx);
quadr = numx * numx;
NSLog(#"Il quadrato del tuo numero %i è: ", numx, quadr);
}
return 0;
}
The second NSLog reports this error: Data argument not used by format string. Why it create this kind of error? In which way I can solve this error?
More over the run-time of the program finish unexpectly after that the output has written: "Inserisci un numero". When I insert the number requiry, the program not display the number squared as required from the second NSLog. Why I'm having this interrupt? Help me please. I what to understand what is happenend.
The warning you get on that line is correct.
The quadr parameter you pass is not used in the format string. Each parameter you pass need to have a % equivalent in the format string.
Specify the extra parameter in your code sample conform line below:
NSLog(#"Il quadrato del tuo numero %i è %i", numx, quadr);
Related
After printing, if I write the name I get:
Insert a name :Andrea
There is no space before Andrea, even if I put the space in the output. How can I add a space before writing the name?
#include <stdio.h>
int main() {
int string[8];
printf("\nInsert a name : ");
printf(" ");
scanf("%s", string);
printf("\nThe name is : %s", string);
return 0;
}
The code that you provided does not compile because the variable string is an array of integers (and not a string as you might think). And when you input the value of it, you're telling the compiler to expect a string ("%s" in scanf("%s", string")).
Change your string declaration to char string[8] and it should work (with the spacing you want):
Note that the value that goes into string will not contain more than 8 characters.
Actually, you did a small mistake in your code, you declared the string to be an array of int & from the code scanf("%s", string") the compiler expects from the user to enter a string as it contains %s as the format specifier. Hence, the code doesn't compile.
In order to correct this, you should declare string as char string[8] (string containing 8 characters).
The correct code is given below :
#include <stdio.h>
int main() {
char string[8];
printf("\nInsert a name : ");
scanf("%s", string);
printf("\nThe name is : %s", string);
return 0;
}
From the above correction your problem for space between input and output will be solved!
Here, is the output which is received from this correction :
I hope so this explanation will be helpful for you!
If any problem persists then feel free to ask in comments! ;-)
I'm just an amateur programmer...
And when reading, for the second time, and more than two years apart, kochan's "Programming in Objective-C", now the 6th ed., reaching the pointer chapter i tried to revive the old days when i started programming with C...
So, i tried to program a reverse C string function, using char pointers...
At the end i got the desired result, but... got also a very strange behavior, i cannot explain with my little programming experience...
First the code:
This is a .m file,
#import <Foundation/Foundation.h>
#import "*pathToFolder*/NSPrint.m"
int main(int argc, char const *argv[])
{
#autoreleasepool
{
char * reverseString(char * str);
char *ch;
if (argc < 2)
{
NSPrint(#"No word typed in the command line!");
return 1;
}
NSPrint(#"Reversing arguments:");
for (int i = 1; argv[i]; i++)
{
ch = reverseString(argv[i]);
printf("%s\n", ch);
//NSPrint(#"%s - %s", argv[i], ch);
}
}
return 0;
}
char * reverseString(char * str)
{
int size = 0;
for ( ; *(str + size) != '\0'; size++) ;
//printf("Size: %i\n", size);
char result[size + 1];
int i = 0;
for (size-- ; size >= 0; size--, i++)
{
result[i] = *(str + size);
//printf("%c, %c\n", result[i], *(str + size));
}
result[i] = '\0';
//printf("result location: %lu\n", result);
//printf("%s\n", result);
return result;
}
Second some notes:
This code is compiled in a MacBook Pro, with MAC OS X Maverick, with CLANG (clang -fobjc-arc $file_name -o $file_name_base)
That NSPrint is just a wrapper for printf to print a NSString constructed with stringWithFormat:arguments:
And third the strange behavior:
If I uncomment all those commented printf declarations, everything work just fine, i.e., all printf functions print what they have to print, including the last printf inside main function.
If I uncomment one, and just one, randomly chosen, of those comment printf functions, again everything work just fine, and I got the correct printf results, including the last printf inside main function.
If I leave all those commented printf functions as they are, I GOT ONLY BLANK LINES with the last printf inside main block, and one black line for each argument passed...
Worst, if I use that NSPrint function inside main, instead of the printf one, I get the desired result :!
Can anyone bring some light here please :)
You're returning a local array, that goes out of scope as the function exits. Dereferencing that memory causes undefined behavior.
You are returning a pointer to a local variable of the function that was called. When that function returns, the memory for the local variable becomes invalid, and the pointer returned is rubbish.
I'm working with a structure IMAGE_T (shown below, excuse the French) with its own alloc function.
typedef struct {
int nbl; /* nombre de ligne de l'image */
int nbc; /* nombre de colonnes de l’image */
unsigned char **data; /* tableau bidim des pixels de l’image */
} IMAGE_T;
IMAGE_T *alloc_image(int nbl, int nbc){
int taille = nbl*nbc+100;
IMAGE_T * image;
image = (IMAGE_T *) calloc(taille, sizeof(unsigned char));
return image;
}
When going through the debugger, it bugs out stating:
"unhandled exception at: 0xc0000005: access violation reading location 0x00000000."
..which I'm pretty sure relates to alloc_image not functioning properly. Any suggestions?
(And for further info, after declaring an IMAGE_T I'm then use another function that returns IMAGE_T *, which itself contains the function alloc_image within it, in order to allocate the memory. Is there anything wrong with this?)
Thanks
I suspect the reason you're getting an access violation is because you're trying to work with the "data" member which calloc() would have made null when allocating the memory.
That said, I'd like to understand why the "data" member in IMAGE_T is a unsigned char **? Why not simply a unsigned char *? (And then, alloc_image must allocate memory to IMAGE_T and then, within that allocated structure, allocate space for the "data".)
I get a warning saying:
"Format specifies type 'char *' but the argument has type 'char'" for the student variable. I am copying/pasting the code out of a book into xcode and am not sure how to fix this. The only thing that prints in the console is "(lldb)". Any advice
#include <stdio.h>
void congratulateStudent(char student, char course, int numDays)
{
printf("%s has done as much %s Programming as I could fit into %d days.\n", student, course, numDays);
}
int main(int argc, const char * argv[])
{
// insert code here...
congratulateStudent("mark", "Cocoa", 5);
return 0;
}
void congratulateStudent(char *student, char *course, int numDays)
the %s means that you are going to print a string ( array of chars)
and char student this means that student is a char type
so student here is not a pointer to a string
In order to change the student type from char to a string pointer you have to add asterisk to student char *student
In your code you are calling the congratulateStudent with input parameter string "mark". So to support this string the input parameter student should be defined as pointer of string
so you are missing the asterisk in the definition of student
The same thing for course
void congratulateStudent(char *student, char *course, int numDays)
Use Function signature like because you are passing string as argument to function in main but function has character type argument..
I'm doing a small app for evaluating and analyzing transfer functions. As boring as the subject might seem to some, I want it to at least look extra cool and pro and awesome etc... So:
Step 1: Gimme teh coefficients! [A bunch of numbers]
Step 2: I'll write the polynomial with its superscripts. [The bunch of numbers in a string]
So, I write a little C parser to just print the polynomial with a decent format, for that I require a wchar_t string that I concatenate on the fly. After the string is complete I quickly try printing it on the console to check everything is ok and keep going. Easy right? Welp, I ain't that lucky...
wchar_t *polynomial_description( double *polyArray, char size, char var ){
wchar_t *descriptionString, temp[100];
int len, counter = 0;
SUPERSCRIPT superscript;
descriptionString = (wchar_t *) malloc(sizeof(wchar_t) * 2);
descriptionString[0] = '\0';
while( counter < size ){
superscript = polynomial_utilities_superscript( size - counter );
len = swprintf(temp, 100, L"%2.2f%c%c +", polyArray[counter], var, superscript);
printf("temp size: %d\n", len);
descriptionString = (wchar_t *) realloc(descriptionString, sizeof(wchar_t) * (wcslen(descriptionString) + len + 1) );
wcscat(descriptionString, temp);
counter++;
}
//fflush(stdout); //Already tried this
len = wprintf(L"%ls\n", descriptionString);
len = printf("%ls**\n", descriptionString);
len = fprintf(stdout, "%ls*\n", descriptionString);
len = printf("FFS!! Print something!");
return descriptionString;
}
During the run we can see temp size: 8 printed the expected number of times ONLY WHILE DEBUGGING, if I run the program I get an arbitrary number of prints each run. But after that, as the title states, wprintf, printf and fprintf don't print anything, yet len does change its size after each call.
In the caller function, (application:(UIApplication *)application didFinishLaunchingWithOptions:, while testing) I put an NSLog to print the return string, and I dont get ANYTHING not even the Log part.
What's happening? I'm at a complete loss.
Im on XCode 4.2 by the way.
What's the return value from printf/wprintf in the case where you think it's not printing anything? It should be returning either -1 in the case of a failure or 1 or more, since if successful, it should always print at least the newline character after the description string.
If it's returning 1 or more, is the newline getting printed? Have you tried piping the output of your program to a hex dumper such as hexdump -C or xxd(1)?
If it's returning -1, what is the value of errno?
If it turns out that printf is failing with the error EILSEQ, then what's quite likely happening is that your string contains some non-ASCII characters in it, since those cause wcstombs(3) to fail in the default C locale. In that case, the solution is to use setlocale(3) to switch into a UTF-8 locale when your program starts up:
int main(int argc, char **argv)
{
// Run "locale -a" in the Terminal to get a list of all valid locales
setlocale(LC_ALL, "en_US.UTF-8");
...
}