C program crashes

Question

Hi I need some help with debugging my program: It should read from the Console, process the input and give it back out:

The error occures after while(scanf("%15s", input) != EOF) is called the 2nd time. Unfortunately I can't tell you what the error is, because the progam freezes and doesn't give me any Information. I think there is something wrong with the input var (it is passed multiple times)

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <ctype.h>

char* repeat(char c, int n);
char* drawLabel(char* label, int n);
char* drawBarnorm(char* label, int value);
char* drawBar(char* label, double value);

int main(void)
{
    char* input;
    double numIn;
    char buf[] = "";
    char* pOutput = &buf[0];

    while(scanf("%15s", input) != EOF)
    {
        scanf("%lf", &numIn);
        if (numIn > 1)
        {
            if (numIn > 30)
            {
                printf("num to big!\n");
                return 0;
            }

            strcat(pOutput, drawBarnorm(input, (int)numIn));
        } else
            {strcat(pOutput, drawBar(input, numIn));}


        printf("%s\n", pOutput);
    }

    printf("%s\n", pOutput);
    return 0;
}

char* repeat(char c, int n)
{
    char* out = (char*)malloc(sizeof(char)*50);
    int i, len;
    out[0] = '\0';

    for (i = 0; i < n; ++i)
    {
        len = strlen(out);
        out[len] = c;
        out[len+1] = '\0';
    }

    return out;
}

char* drawLabel(char* label, int n)
{
    if (strlen(label) > n)
    {
        char* newLabel = (char*)malloc(sizeof(char)*(n+1));
        newLabel[0] = '\0';
        strncpy(newLabel, label, n);
        newLabel[n] = '\0';
        return newLabel;
    } else if (strlen(label) < n)
    {
        strcat(label, repeat(' ', n-strlen(label)));
    }

    return label;
}

char* drawBarnorm(char* label, int value)
{
    char* bar = (char*)malloc(sizeof(char)*41);
    char* barPart;
    bar[0] = '\0';
    bar = drawLabel(label, 8);
    strcat(bar, "|");
    barPart = drawLabel(repeat('#', value), 30);
    strcat(bar, barPart);
    strcat(bar, "|");
    return bar;
}

char* drawBar(char* label, double value)
{
    int val = (int)(30.0*value);
    return drawBarnorm(label, val);
}

Thank you for helping me out with this.

You made the exact same mistake in this question as previous. — Sadique
– Sadique, Commented Jan 8, 2015 at 17:32
Those who cannot remember the past are condemned to repeat it. -- George Santayana. — Paul R
– Paul R, Commented Jan 8, 2015 at 17:38
this line: 'while(scanf("%15s", input) != EOF)' contains an error. What the code really wants to look for is 'was the input/conversion successful?' therefore, the correct way to write the line would be: 'while( 1 == scanf(" %15s", input))' I.E. 1 input conversion and leading ' ' in format string to skip over/absorb any leading white space, (like a newline). — user3629249
– user3629249, Commented Jan 8, 2015 at 18:01
the function: drawlabel() returns a pointer to a malloc'd area, so the line: 'bar = drawLabel(label, 8);' overlays the prior contents of 'bar', resulting in a memory leak because 'bar' was already set by a pointer to some malloc'd memory area — user3629249
– user3629249, Commented Jan 8, 2015 at 18:04
I rolled back your question as your edit make the answers invalid (you corrected what was wrong). When you get the answer that solves your problem you should mark it as accepted, don't edit your question. — bolov
– bolov, Commented Jan 8, 2015 at 18:16

Gopi · Accepted Answer · 2015-01-08 17:28:34Z

4

char* input = malloc(size); /* Allocate memory of your wish */

Allocate memory to input You have not initialized your pointer.

The pointer should be pointing to some valid memory location to store the value through scanf()

answered Jan 8, 2015 at 17:28

Gopi

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3 Comments

Iharob Al Asimi Over a year ago

You know there is a free function right? And what should the value of size be?

user3629249 Over a year ago

in the main() function, 'input' is defined as 'char input[40]' so the scanf is ok. (other than needed to check the returned value to assure the input/conversion was successful

David Conrad Over a year ago

@user3629249 Why do I see char* input; in main()?

Iharob Al Asimi · Accepted Answer · 2015-01-08 17:47:42Z

3

You have to initialize input or declare it as an array like this

char input[16];

also, you should notice that scanf does not return EOF it returns the number of arguments matched, so you have to change

while(scanf("%15s", input) != EOF)

to

while(scanf("%15s", input) == 1)

because while(scanf("%15s", input) != EOF is always true.

edited Jan 8, 2015 at 17:47

answered Jan 8, 2015 at 17:28

Iharob Al Asimi

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3 Comments

user3025417 Over a year ago

Thx, that helped a lot. after I exit with an EOF I get a: STATUS_ACCESS_VIOLATION.

user3025417 Over a year ago

Aha thats funny because I can exit the loop with EOF.

Iharob Al Asimi Over a year ago

No you can't. The character sent is not what scanf returns, in that case it returns 0, but since 0 != EOF you enter the loop with input uninitialized, then when you trying to access input it's UNDEFINED BEHAVIOR which in your case is causing STATUS_ACCESS_VIOLATION apparently.

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