I am trying to convert some code that is meant to remove all non-numeric characters except for "_" from a command line argument, except instead of a command line argument I am trying to get the code to accept input from a regular string, I've tried to convert the code to accept strings, but i keep getting this error
words.c:9: warning: assignment makes pointer from integer without a cast
I am confused as to what I am doing wrong so I would really appreciate any help that I can get with this problem, thanks!
Also here is the original code that accepts command line arguments
#include <stdio.h>
#include <string.h>
#include <ctype.h>
int main(int argc, char ** argv) {
int i;
char *p;
if (argc > 1) {
for (p = argv[1]; *p != '\0'; p++) {
if (islower(*p) || isdigit(*p) || *p == '_') {
putchar (*p);
}
}
putchar ('\n');
}
return 0;
}
and here is my "version"
#include <stdio.h>
#include <string.h>
#include <ctype.h>
int main(void) {
int i;
char *p;
char stg[] = "hello";
// if (argc > 1) {
for (p = stg[1]; *p != '\0'; p++) {
if (isalnum(*p) || *p == '_') {
putchar (*p);
}
}
putchar ('\n');
return 0;
}
In your code p is a pointer. Change p = stg[1]; to p = &stg[1];.
Related
I have found some information about strcat and experimented with it but it doesn't work the way i expected for example :
char a = 'a', b = 'b';
strcat(a,b);
printf("%c", a);
this will produce an error "initialization of 'char' from 'char *' makes integer from pointer without a cast". Is there a way to unite chars until the wanted word is complete and store it in 1 variable? Or am i going completely wrong about this. The purpose of the code is to read an xml file and build a tree with the tags.
Any help is or advice is very much appreciated.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main() {
int count = 0;
char c, word;
FILE *file = fopen("example.xml", "r");
if (file == NULL) {
return 0;
}
do {
c = fgetc(file);
if (c == '<') {
count = 1;
}
if (c == '>') {
count = 0;
printf(">");
}
if (count == 1) {
printf("%c", c);
}
if (feof(file)){
break ;
}
} while(1);
fclose(file);
return(0);
}
I'm not sure exactly what you're trying to accomplish, but you could try something like the following, which will print every <tag>, i.e., every string in the file between <...>'s , and will also accumulate them in an array of strings called tags[]. And note that you'd might want to add checks that avoid going over the 99 chars/tag and 999 tags total. But if this isn't anything like what you're actually trying to do, maybe clarify the question.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main() {
int ntags=0, ichar=0,nchars=0;
char c='\000', tags[999][99];
FILE *file = fopen("example.xml","r");
if (file==NULL) return(0);
while((ichar=fgetc(file))!=EOF) {
c = (char)ichar;
if (nchars==0 && c!='<') continue;
tags[ntags][nchars++] = c;
if (c=='>') {
tags[ntags][nchars] = '\000';
printf("tag#%d = %s\n",ntags+1,tags[ntags]);
nchars=0; ntags++; }
}
/* do you now want to do anything with your tags[] ??? */
fclose(file);
return(0);
}
You are trying to use a function, those parameters are char *
char *strcat(char *dest, const char *src)
but you gave strcat a char but it wants a char*
int main()
{
char str1[20] = "this";
char str2[] = "is";
strcat(str1, str2);
printf("%s", str1);
return 0;
}
this is the way i thinkt you want it
I've been working on a function which censors words. I've created this function and it works, except that it only accepts one argument. For example, when I do "./a.out test < example.txt", it replaces "test" with CENSORED in "example.txt". But when I add another one, like "./a.out test test2 < example.txt", it only replaces "test", not both "test" and "test2".
Can someone help me with my function please? I don't know what I'm doing wrong.
Here's the function:
#include <assert.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main(int argc, char **argv)
{
assert(argc > 1);
char fileRead[4096];
char replace[] = "CENSORED";
size_t word_len = strlen(argv[1]);
while (fgets(fileRead, sizeof(fileRead), stdin) != 0)
{
char *start = fileRead;
char *word_at;
while ((word_at = strstr(start, argv[1])) != 0)
{
printf("%.*s%s", (int)(word_at - start), start, replace);
start = word_at + word_len;
}
printf("%s", start);
}
printf("\n");
return (0);
}
I suggest you put in a middle loop over argv elements 1 to argc - 1. In each iteration, it would process the line to censor the corresponding argument, just as your function now does only for the first argument.
int arg;
for (arg = 1; arg < argc; arg += 1) {
/* ... censor argv[arg] ... */
}
Note that you can then drop the assert(), too, as structuring the argument access that way naturally avoids accessing the argv array outside its bounds (if no arguments are specified, the program will run without censoring anything).
In this function I am going to be receiving char * words such as
person.vet.blah
and
word.friends.joe
I want to extract the first word. So for the first one I want to extract
person
and the second one I want to extract
word
How can I correctly do this? Here is my code:
char *separate_name(char *machine_name)
{
//iterate until you find period. then return
char absolute_name[1000];
int i;
for (i =0; i < strlen(machine_name); i++)
{
if (machine_name[i] == '.')
absolute_name[i] = machine_name[i];
}
return absolute_name;
}
This is just segfaulting. Any ideas what I should be doing? machine_name is going to be the "person.vet.blah" and then return absolute_name which would be "person"
Fixing your code
As others have pointed out, you can't use absolute_name outside of the function in which it was defined. This is because you're when you return the variable from your function, all that is being returned is a pointer to the beginning of the array. Outside the function, the array itself no longer exists, so the pointer is invalid and you get a segfault if you try and dereference it.
You can get around this by using malloc. Don't forget to free the memory you have allocated when you are done using it.
By the way, as well as changing your loop to a while, I also fixed the check (you were checking machine_name[i] == '.', the opposite to what you wanted).
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
char *separate_name(char *machine_name)
{
// allocate memory on the heap
char *absolute_name = malloc(strlen(machine_name)+1);
int i = 0;
while (i < strlen(machine_name) && machine_name[i] != '.') {
absolute_name[i] = machine_name[i];
++i;
}
absolute_name[i] = '\0';
return absolute_name;
}
int main()
{
char name1[] = "person.vet.blah";
char *first1 = separate_name(name1);
if (first1 != NULL) {
printf("%s\n", first1);
free(first1);
}
char name2[] = "word.friends.joe";
char *first2 = separate_name(name2);
if (first2 != NULL) {
printf("%s\n", first2);
free(first2);
}
return 0;
}
A better alternative
strtok is the perfect tool for the job:
#include <stdio.h>
#include <string.h>
char *separate_name(char *machine_name)
{
return strtok(machine_name, ".");
}
int main()
{
char name1[] = "person.vet.blah";
char *first1 = separate_name(name1);
if (first1 != NULL) printf("%s\n", first1);
char name2[] = "word.friends.joe";
char *first2 = separate_name(name2);
if (first2 != NULL) printf("%s\n", first2);
return 0;
}
As pointed out in the comments (thanks #John), strtok modifies the string that is passed to it (it replaces the delimiter . by the \0 null byte to mark the end of the string). This isn't a problem here but is something to be aware of.
Output using either program:
person
word
#include <stdio.h>
char *separate_name(const char *machine_name){
static char absolute_name[1000];
int i;
for (i =0; i < sizeof(absolute_name)-1 ; i++){
if(machine_name[i] == '.' || machine_name[i] == '\0'){
absolute_name[i] = '\0';
break;
} else {
absolute_name[i] = machine_name[i];
}
}
return absolute_name;
}
int main(void){
printf("%s\n", separate_name("person.vet.blah"));
printf("%s\n", separate_name("word.friends.joe"));
return 0;
}
My code is giving me a segmentation fault. I'm 99% sure the fault is stemming from my lousy code construction.
#include <stdio.h>
#include <assert.h>
#include <string.h>
int decToBit(unsigned int I, char *str){
str = "";
int currentVal = I;
do{
if(I%2 == 0)
strcat(str,"0");
else
strcat(str,"1");
} while(currentVal > 0);
return(0);
}
You need to make sure that there is enough space in str to add the extra characters:
char myStr[200];
myStr[0] = '\0'; // make sure you start with a "zero length" string.
strcpy(myStr, str);
and then use myStr where you were using str.
As it is, the statement
str="";
points str to a const char* - that is a string you can read but not write.
Incidentally the call signature for main is
int main(int argc, char *argv[])
in other words, you need a pointer to a pointer to char. If I am not mistaken, you would like to do the following (a bit of mind reading here):
Every odd argument gets a 1 added; every even argument gets a 0 added.
If my mind reading trick worked, then you might want to try this:
#include <stdio.h>
#include <string.h>
int main(int argc, char * argv[]) {
char temp[200];
temp[0] = '\0';
int ii;
for(ii = 0; ii < argc; ii++) {
strncpy(temp, argv[ii], 200); // safe copy
if(ii%2==0) {
strcat(temp, "0");
}
else {
strcat(temp, "1");
}
printf("%s\n", temp);
}
}
edit just realized you edited the question and now your purpose is much clearer.
Modified your function a bit:
int decToBit(unsigned int I, char *str){
str[0] = '\0';
char *digit;
do
{
digit = "1";
if ( I%2 == 0) digit = "0";
strcat(str, digit);
I>>=1;
} while (I != 0);
return(0);
}
It seems to work...
In do-while loop you should increment the value of currentVal. Otherwise it will be an infinity loop and you will end up with Segmentation fault.
Initialize str[0] properly.
Divide I by 2 each loop.
But then the string will be in a little endian order. Doubt that was intended?
int decToBit(unsigned int I, char *str) {
str[0] = '\0';
do {
if (I%2 == 0)
strcat(str,"0");
else
strcat(str,"1");
I /= 2;
} while(I > 0);
return(0);
}
// call example
char buf[sizeof(unsigned)*CHAR_BIT + 1];
decToBit(1234567u, buf);
#include <stdio.h>
#include <string.h>
#include <limits.h>
#include <assert.h>
char *decToBit(unsigned int I, char *str){
int bit_size = CHAR_BIT * sizeof(I);
str += bit_size;
*str = 0;
do{
*--str = "01"[I & 1];
}while(I>>=1);
return str;
}
int main(){
char bits[33];
printf("%s\n", decToBit(0, bits));
printf("%s\n", decToBit(-1, bits));
printf("%s\n", decToBit(5, bits));
return 0;
}
I am working on some code that filters text before it is sent further into a program (this code removes everything but all alphanumeric characters and and underscores), the code itself works perfectly except for the fact that I cannot find a way to store the output of of it for use in other parts of the program, If i had to guess, this probably involves saving the stdout from putchar into a variable, but i cannot find much info for doing so online, if someone could point me in the right direction for this I would really appreciate it, thanks!
#include <stdio.h>
#include <string.h>
#include <ctype.h>
int main(void) {
int i;
char *p;
char stg[] = "hello";
for (p = &stg[0]; *p != '\0'; p++) {
if (isalnum(*p) || *p == '_') {
putchar (*p);
}
}
putchar ('\n');
return 0;
}
Perhaps I don't understand your "need" to use putchar() while doing the filtering, but you can filter the input into an output array of chars to use however needed after the filtering as shown below.
#include <stdio.h>
#include <string.h>
#include <ctype.h>
int main(void) {
int i;
char *p;
char stg[] = "hel123*^_lo";
char output[200] = {0x00};
int index = 0;
p = stg;
while( *p )
{
if (isalnum(*p) || *p == '_')
{
output[index++] = (char)putchar(*p);
}
p++;
}
putchar('\n');
printf("[%s]\n", output);
return 0;
}
Output:
hel123_lo
[hel123_lo]
EDIT:
And if you want to just filter the string into an array without displaying the string using putchar() you'd do something like this:
#include <stdio.h>
#include <string.h>
#include <ctype.h>
int main(void) {
int i;
char *p;
char stg[] = "hel123*^_lo";
char output[200] = {0x00};
int index = 0;
p = stg;
while( *p )
{
if (isalnum(*p) || *p == '_')
{
output[index++] = *p;
}
p++;
}
printf("[%s]\n", output);
return 0;
}
And what exactly are you trying to do with the output of the filtered text?
putchar -- int putchar( int ch ); -- returns the character you wrote if successful, EOF if failure.
Nothing prevents you from declaring an int variable, whether a scalar variable, an array element, or a field in a struct, and saving what you wrote. Take note, the return is an int, not a char.
Based on what you've written, you'll probably have to write some code to manage all the outputs you save. In other words, if I'm interpreting your question correctly, you'll be doing more than just saving what you wrote to a variable. You'll probably want to say where in the code you executed the putchar and perhaps even the time. Just guessing though.