I am trying to calculate result of the floor function for floats <= 9999.
#include <stdlib.h>
include <stdio.h>
#include "string.h"
int main(int argc, char* argv[]) {
int i, j, k;
int x[1000];
for(i = 0; i < 10000; ++i){
x[i] = i;
}
printf("Enter a float in 0..9999: ");
scanf("%d", k);
tester(x, k);
}
int tester(int* c, int k) {
printf("x[%d] = %d\n", k, c[k]);
}
When compiler came to;
for(i = 0; i < 10000; ++i){
x[i] = i;
}
it gives segmentation fault;
x[i] = i;
here.
I have already checked similar questions about assigning segmentation fault but I couldn't find any solution way. Can anyone help?
The array x is of length 1,000, but you're treating it in the loop as if it's of length 10,000. Accessing x[i] for i greater than or equal to 1,000 is undefined behaviour because the index is out of the array's range.
Thus, a segmentation fault is occurring because your program is accessing memory that it is not allowed to access.
The variable k is initialised and when getting input "&" is missing in the scanf statement. This might have come under segmentation fault since the value "k" is passed in the function tester(). Generally in C lang, we get input with "&", unless if it is a string you don't necessarily mention that in the scanf statement!!.
Related
Wrote a program that multiply two arrays like this:
uv = u1v1 + u2v2 + u3v3 + ... un*vn
after getting from the user both of the arrays, i get a "signal: segmentation fault (core dumped)" error.
here's the code:
#include <stdio.h>
int scalar_product(int vectorU[], int vectorV[], int vectorLength) {
int i, sum = 0;
for (i = 0; i < vectorLength; i++)
sum += (vectorU[i] * vectorV[i]);
return sum;
}
void userInterface() {
int vectorLength = 0, i;
printf("Please enter the length of the vectors: ");
scanf("%d", &vectorLength);
int vectorU[vectorLength], vectorV[vectorLength];
printf("\nVector U:");
for (i = 0; i < vectorLength; i++) {
printf("\n%d) ", (i + 1));
scanf("%d", &vectorU[i]);
}
printf("\nVector V:");
for (i = 0; i < vectorLength; i++) {
printf("\n%d) ", (i + 1));
scanf("%d", &vectorV[i]);
}
printf(scalar_product(vectorU, vectorV, vectorLength));
}
main(void) {
userInterface();
}
This call of printf is incorrect
printf(scalar_product(vectorU, vectorV, vectorLength));
You need to write at least
printf( "%d\n", scalar_product(vectorU, vectorV, vectorLength));
Also it would be better to declare and define the function like
long long int scalar_product( const int vectorU[], const int vectorV[], int vectorLength) {
long long int sum = 0;
for ( int i = 0; i < vectorLength; i++)
sum += ( long long int )vectorU[i] * vectorV[i];
return sum;
}
To output the result you need to use the format string "%lld\n"..
The type long long int is used to avoid an overflow.
Another way is to declare the function return type as double.
Also you forgot to specify the return type int of the function main.
Here:
printf(scalar_product(vectorU, vectorV, vectorLength));
... you have failed to specify a format for printf. As a result, it attempts to interpret the result of scalar_product() as a pointer to the format string. Undefined behavior results.
If your compiler is not emitting a warning about that then you should either learn how to turn up the warning level so that it does, or else get a better compiler. If your compiler is emitting a warning about it, then take this as a lesson that it is not safe to ignore compiler warnings.
Probably you wanted somethign more like this:
printf("%d\n", scalar_product(vectorU, vectorV, vectorLength));
As a minor additional issue, you have forgotten the return type for main(). Your compiler is probably treating it as returning int, which turns out to be the right thing to do, but that doesn't make your code correct. You want:
int main(void) {
// ...
With those two changes, your program compiles for me without any diagnostics, and runs without error, producing the result I expect.
At least, for small vector lengths. If you try really large vectors then you might exceed the available space for allocating your vectors on the stack.
I just have a function that finds out the maximum value of an array of integers, but I get a segmentation fault, which I can't find because the compiler doesn't show me the line of the error.
This is my C code:
#include <stdlib.h>
#include <stdio.h>
//Funktion ermittelt den größten Wert eines Arrays
int groesstesElement(int **arrayPointer){
int max = 0;
for (int i = 0; i < 3; i++) {
if (*arrayPointer[i]>max) {
max = *arrayPointer[i];
}
}
return max;
}
int main (int argc, char **argv) {
int array[4]={1,2,3,4};
int *ptr = array;
int z = groesstesElement(&ptr);
printf("%d\n", z);
return EXIT_SUCCESS;
}
I use macOS and VSC.
In C, array indexing [] has higher precedence than pointer de-referencing *: https://en.cppreference.com/w/c/language/operator_precedence
Some parentheses fix the segfault.
if ((*arrayPointer)[i]>max) {
max = (*arrayPointer)[i];
}
Due to the operators precedence, with
*arrayPointer[i]
you are telling your program:
Take the i-th element of the array arrayPointer and dereference it.
But arrayPointer is a pointer to int *, so all you get is the address of ptr (the int ** pointer defined from main) with an offset. When you finally dereference it you are likely accessing an invalid address, causing segmentation fault.
As already suggested by the main answer, the fix is done using parenthesis in order to apply the operators in the order you want:
(*arrayPointer)[i]
Secondary issues in the code
Even though with the correction above the program won't crash anymore, it won't work. Searching through the array with the loop
for (i = 0; i < 3; i++)
you won't include the last item in the search (index 3), skipping precisely the index that, in your example, contains the maximum value. You probably meant for (i = 0; i < 4; i++) or for (i = 0; i <= 3; i++).
Anyway, using magic numbers in the code (in this case the dimension of the array) is considered bad practice. A better solution would have been using a #define, but an even better solution would have been passing to the function the size of the array:
#include <stdlib.h>
#include <stdio.h>
#define ARR_SIZE 4
//Funktion ermittelt den größten Wert eines Arrays
int groesstesElement(int *arrayPointer, unsigned int arrSize){
int max = 0, i;
for (i = 0; i < arrSize; i++) {
if (arrayPointer[i]>max) {
max = arrayPointer[i];
}
}
return max;
}
int main (int argc, char **argv) {
int array[ARR_SIZE]={1,2,3,4};
int z = groesstesElement(array, ARR_SIZE);
printf("%d\n", z);
return EXIT_SUCCESS;
}
Please note how there's no need to use a double pointer anymore.
Basically I have a function called MinSubTab that is supposed to calculate the sum of the array passed and also to change the value passed in the first argument from inside the function without using return. This is done with pointers. Anyway, I think it'd be easier if I just showed you the code so here it is:
maintab.c
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include "tab.h"
int main(){
int *reftab;
int min;
reftab = (int *)malloc(sizeof(int) * NMAX);
InitTab(reftab,NMAX);
printf("\n Total: %d et min: %d", MinSumTab(&min, reftab, NMAX), min);
free(reftab);
return 0;
}
tab.c
void InitTab(int *tab, int size){
srand(time(NULL));
for (int i=0; i<size; i++){
*(tab+i) = rand() % 10;
}
}
int MinSumTab(int *min, int *tab, int size){
int total=0;
int minimum = NMAX;
int temp = *min;
for (int i=0; i<size; i++){
total += *(tab+i);
}
for (int i=0; i<size; i++){
if(*(tab+i)<minimum){
minimum = *(tab+i);
}
}
*min = minimum;
return total;
}
So the expected result here is that the sum is printed (which it is) and the minimum value of the array is printed (which it is not). Every single time the min variable equals 8 and I've no idea how to actually change the value of min from within that function.
Please help as my brain has no more capacity for rational thought, it's been 1.5 hrs and no solution in sight. Thanks
Looks like a small mistake:
You initialize minimum with NMAX, which I assume is 8 (the size of the array). 99.9% of the random numbers will be bigger. So 8 is chosen as the minimum.
What you really want is to initialize it with RAND_MAX – the maximum value rand() can return.
In C order of evaluation and argument passing is undefined.
You can of course the order yourself but it only to feed your curiosity.
#include <stdio.h>
volatile char *message[] = {
"fisrt", "second", "third", "fourth"
};
int print(size_t x)
{
printf("%s\n", message[x]);
return x;
}
int main()
{
printf("%d %d %d %d\n", print(0), print(1), print(2), print(3));
return 0;
}
Note. There is one exception from this rule.
Logical operators are evaluated form the left to the right.
if( x != NULL && *x == 5)is safe because x will not be dereferenced if it is NULL
I am struggling with specific parts in my code that I seem to have formatted wrong. This code was taken from my programming book and the parts that were blank have a '$' around them. However, there are two blanks I can't seem to figure out. My current code is:
int sum_two_dimensional(const int a[][LEN], int n)
{
int i,j, sum = 0;
for(i=0, i<n; i++)
for(j = 0; j< LEN; j++)
sum+=a[i][j];
return sum;
}
int sum_two_dimensional_array(const in a[][LEN], int n)
{
int *p, sum = 0;
for(p= a[0]; p < a[0] ______; p++)
sum += ________; //my guess is a[p][sum];
return sum;
}
I tried several things in these blanks an it seems that I keep getting errors. I do not fully understand the array/pointer situation. The blanks that I filled in, (encased in $$$), I feel are right but feel free to double check me. I appreciate any help.
This exploits the fact that an array a[N][M] uses the same memory as a single dimension array a[N*M]
So you can "safely" iterate a[0] "out of bound" without triggering memory exception up to the index a[0][N*M-1]
int sum_two_dimensional_array( int a[][LEN], int n)
{
int *p, sum = 0;
for(p= a[0]; p < a[0]+n*LEN; p++)
sum += *p;
return sum;
}
My Code:
#include <stdio.h>
int main(int argc, char*argv[]){
int n = argc;
int i, a, b, sum;
for(i = 0; i < n; i++){
sscanf(argv[i], "%u", &a);
b = a + sum;
sum = b;
}
printf("%d\n", sum);
return 0;
}
This piece of code should do ./a 0 1 2 3 must write terminal 6 But writes 42423.
The aim of the program was to issue the command-line arguments amount. But he does not make it correct angulation.
argv[0] holds the name of the executable which most likely you don't want to include in the loop. so, you need to start the loop from i=1.
As per your input, the argv[0] does not contain a numeric value hence causing a failure to sscanf(), leaving a uninitialized.
So, in your code, the primary issue is with,
b = a + sum;
where, for the first iteration, a and sum are both uninitialized local variables having indeterminate value. So, for the very first loop, you're invoking undefined behavior.
Also, a being an int, you need to use %d format specifier for it.
Two things to mention:
Always check for the return value of scanf() family for success.
Always initialize your local variables.
You are getting garbage value because you are not initialized varuiable sum on declaration.
Just initialize is as sum = 0 and u will get expected result.
Or u can use below code also.
#include <stdio.h>
#include <stdlib.h>
int main(int argc, char*argv[]){
int n = argc;
int i, a, b, sum=0;
for(i = 0; i < n; i++){
a = atoi(argv[i]);
sum += a;
}
printf("%d\n", sum);
return 0;
}