this is my first time posting to this forum so if I neglect any formalities or bother anyone in any way with something similar please let me know and I'll do my best to avoid doing it again!
I am trying to generate two arrays using the following code, but I am having a problem actually outputting the code. I know this is probably something very basic, but I just started using C only about two weeks ago. I'm quite sure everything is correct, but for some reason when I try to compile the code while linking the math library with gcc static.c -lm -o static and then when I further ask for the output using ./static, I am given no output and am asked for the next command. What am I doing wrong?
If this is something simple or an oversight then the odds are I am missing something conceptually and if you wouldn't mind elaborating on it I would really appreciate it. thank you!
#include <stdio.h>
#include <stdlib.h>
#define N 100
#define pi 3.14
#include <math.h>
int main (void) {
double x[N], f[N];
int i;
for (i = 0; i < N; i++) {
x[i] = (double)(i) / ((double)(N) - 1.0);
f[i] = sin(2.0 * pi * x[i]);
}
return EXIT_SUCCESS;
printf("x is %f",x[i]);
}
You already return success and the code below will not be executed. Swap the two statements.
printf("x is %f",x[i]);
return EXIT_SUCCESS;
Your printf is after the return, so your code doesn't actually reach it. You need to have it before.
Related
I am having an extraordinary problem with my current Code::Blocks (GNU GCC compiler) setup. The compiler seems to selectively run some GSL functions, but seems for some reason to have great problems when commanded to execute other GSL functions.
For example, I have lifted the following code from the following destination:
https://www.gnu.org/software/gsl/manual/html_node/Example-programs-for-matrices.html
I assume that because the code is derived from the official GNU website, that the code is correct:
#include <math.h>
#include <stdio.h>
#include <gsl/gsl_matrix.h>
#include <gsl/gsl_blas.h>
int
main (void)
{
size_t i,j;
gsl_matrix *m = gsl_matrix_alloc (10, 10);
for (i = 0; i < 10; i++)
for (j = 0; j < 10; j++)
gsl_matrix_set (m, i, j, sin (i) + cos (j));
for (j = 0; j < 10; j++)
{
gsl_vector_view column = gsl_matrix_column (m, j);
double d;
d = gsl_blas_dnrm2 (&column.vector);
printf ("matrix column %d, norm = %g\n", j, d);
}
gsl_matrix_free (m);
return 0;
}
From debugging, I have learned that the source of the error is the following line:
d = gsl_blas_dnrm2 (&column.vector);
The compiler crashes at this point and prints the following error message:
Process returned -1073741819 <0xC0000005>
I have spent a lot of time trying to discover the source of the bug but have sadly not had much success. I am generally not sure why there is a crash at all. The debugger prints no warnings or error messages.
I'm going to suggest that perhaps you have mismatched headers and libraries. Perhaps there is more than one version of GSL installed. You have the headers from one version referenced in your source, and the linker is referencing the libs from other version.
I went looking up the typedef of the gsl_vector_view and ended up here, and you may be even able to discern that this version doesn't even support the vector member of that struct type.
You will get this 0xC0000005 error, typically when you use some unitialised pointer. Its not that your pointer is uninitialised here though .. I'd say what's happening is the 'vector' bit of &column.vector is being interpreted as something other than what is intended.
In summary, I think this is some kind of environmental issue, perhaps with your linker settings? There are some details on how to configure these here: http://www.learncpp.com/cpp-tutorial/a3-using-libraries-with-codeblocks/
Hope this helps.
I am new to C programming and I am currently learning loops. In the below program,
#include<stdio.h>
main()
{
int i;
for(i=1;i++<=5;printf("%d",i));
}
i tried to compile in dev c++ compiler but it is giving error "[Error] ld returned 1 exit status"
You need to include the <stdio.h> header, and also, main needs a return type (int) and a return value. Changing the program to this will make it compile (at least it did using GCC) and run:
#include <stdio.h>
int main(int argc, char *argv[])
{
int i;
for(i=1;i++<=5;printf("%d",i));
return 0;
}
The quotes you used in the “%d” are illegal too, use normal quotes: "%d".
Apart from that, doing the printf inside the loop head might be legal, but it's pretty bad style. Usually in a for-loop you would have have initialization;condition;increment(or decrement or w/e) in the head, and do side-effects in the body of the statement.
I would try writing the for loop as:
for(i=1;i < 6;i++) { printf(“%d”,i); }
I have run this program manually on my notebook and i got Output 23456
Then i run this on Dev c++ and it is giving the same output 23456 without any error and i have just copied and pasted from ur question dun know why its showing error on ur runtime may be u have not saved it as C file
I want to use atoi function in my program, but I found it not working.
#include <ctype.h>
int value;
value=atoi(buf);
char buf points to "1000" or something like, terminated by \0. I have checked it.
But the value evaluates always to zero. I have tried strtol(), but I get the same error.
My ADS (ARM Developer Suit) is v1.2 (s3c2440). I can find the libs in armlib path (c_t_xx.l).
I use axd debug mode, so I can trace my code. I found "bl
__rt_ctype_table", so I think asm code linked right.
Please give any advice to fix this issue.
ARM might have a problem with string functions, you haven't mentioned whether it returns a value and it's incorrect (i heard it's a bug and it's better you should write the function on your own) or there is no value at all.
anyway look at the arm article about it i think it's the solution - ARM article about string functions
The following code should work,
#include <stdio.h>
#include <stdlib.h>
int main()
{
int i;
char buff[5] = "1000\0";
i=atoi(buff);
printf("i=%d\n", i);
return 0;
}
#./a.out
#i=1000
I have recently started learning C as a side project. I am working under OpenSuse with the latest NetBeans using the GCC as toolset for compiling.
One of the very first programs that I made was this:
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
/*
*
*/
int main(int argc, char** argv) {
double rad = 1;
double result = 0;
result = sin(rad);
return (EXIT_SUCCESS);
}
This is a simple, no-brainer example that should have worked without a problem. However, I get a Build Error: Exit code 2(error in line 18, undefined reference to sin) when trying to compile.
Interestingly enough, if I remove the assignment of the value of sin(rad) to result OR replace rad with a hard coded value, the program compiles just fine.
What am I doing wrong here?
In C, you need to link to the math library:
Add this to the command line options:
-lm
Be sure that your are linking with the math library.
$ gcc myprog.c -lm
A simple C program which uses gettimeofday() works fine when compiled without any flags ( gcc-4.5.1) but doesn't give output when compiled with the flag -mno-sse.
#include <stdio.h>
#include <stdlib.h>
int main()
{
struct timeval s,e;
float time;
int i;
gettimeofday(&s, NULL);
for( i=0; i< 10000; i++);
gettimeofday(&e, NULL);
time = e.tv_sec - s.tv_sec + e.tv_usec - s.tv_usec;
printf("%f\n", time);
return 0;
}
I have CFLAGS=-march=native -mtune=native
Could someone explain why this happens?
The program returns a correct value normally, but prints "0" when compiled with -mno-sse enabled.
The flag -mno-sse causes floating point arguments to be passed on the stack, whereas the usual x86_64 ABI specifies that they should be passed via SSE registers.
Since printf() in your C library was compiled without -mno-sse, it is expecting floating point arguments to be passed in accordance with the ABI. This is why your code fails. It has nothing to do with gettimeofday().
If you wish to use printf() from your code compiled with -mno-sse and pass it floating point arguments, you will need to recompile your C library with that option and link against that version.
It appears that you are using a loop which does nothing in order to observe a time difference. The problem is, the compiler may optimize this loop away entirely. The issue may not be with the -mno-sse itself, but may be that that allows an optimization that removes the loop, thus giving you the same time each time you run it.
I would recommend trying to put something in that loop which can't be optimized out (such as incrementing a number which you print out at the end). See if you still get the same behavior. If not, I'd recommend looking at the generated assembler gcc -S and see what the code difference is.
The datastructures tv_usec and tv_sec are usually longs.
Redeclaration of the variable "time" as a long integer solved the issue.
The following link addresses the issue.
http://gcc.gnu.org/ml/gcc-patches/2006-10/msg00525.html
Working code:
#include <stdio.h>
#include <stdlib.h>
int main()
{
struct timeval s,e;
long time;
int i;
gettimeofday(&s, NULL);
for( i=0; i< 10000; i++);
gettimeofday(&e, NULL);
time = e.tv_sec - s.tv_sec + e.tv_usec - s.tv_usec;
printf("%ld\n", time);
return 0;
}
Thanks for the prompt replies. Hope this helps.
What do you mean doesn't give output?
0 (zero) is a perfectly reasonable output to expect.
Edit: Try compiling to assembler (gcc -S ...) and see the differences between the normal and the no-sse version.