I have a problem with my C program. It's a command line argument of searching character string form the text file and output the line started with the user input character without using strstr(). It's OK but there is one problem. I want to output the whole file when Search Character is NULL. When I did this, the output become different of using strstr() build-in function. Can you help me what's wrong with my code, please?
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
char* MyStrstr(char* pszSearchString, char* pszSearchWord);
int main(int argc, char* argv[])
{
char szTemp1[10] = {0};
char szTemp2[10] = {0};
char * pszTemp1 = NULL;
char * pszTemp2 = NULL;
strcpy(szTemp1, "aabaaacaaaad");
strcpy(szTemp2, "");
pszTemp1 = MyStrstr(szTemp1, szTemp2);
pszTemp2 = strstr(szTemp1, szTemp2);
printf("%s\n",pszTemp1);
printf("%s", pszTemp2);
return 0;
}
char* MyStrstr(char* pszSearchString, char* pszSearchWord) {
int nFcount = 0;
int nScount = 0;
int nSearchLen = 0;
int nIndex = 0;
char* pszDelString = NULL;
if(pszSearchString == NULL) {
return NULL;
}
if(pszSearchWord == ""){
return pszSearchString;
} else {
while(pszSearchWord[nSearchLen] != '\0') {
nSearchLen++;
}
for(nFcount = 0; pszSearchString[nFcount] != '\0'; nFcount++) {
if(pszSearchString[nFcount] == pszSearchWord[nScount]) {
nScount++;
} else {
nScount = 0;
}
if(nScount == nSearchLen) {
nIndex = (nFcount - nScount) + 1;
pszDelString = pszSearchString + nIndex;
}
return pszDelString;
}
}
return NULL;
}
Replace
if(pszSearchWord == "")
by
if (pszSearchWord[0] == 0)
pszSearchWord == "" compares the address pszSearchWord to the address of the string literal "" and those addresses are always different in your case. You cannot compare strings using the == operator.
Related
I'm fairly new to C programming, how would I be able to check that a string contains a certain character for instance, if we had:
void main(int argc, char* argv[]){
char checkThisLineForExclamation[20] = "Hi, I'm odd!"
int exclamationCheck;
}
So with this, how would I set exclamationCheck with a 1 if "!" is present and 0 if it's not? Many thanks for any assistance given.
By using strchr(), like this for example:
#include <stdio.h>
#include <string.h>
int main(void)
{
char str[] = "Hi, I'm odd!";
int exclamationCheck = 0;
if(strchr(str, '!') != NULL)
{
exclamationCheck = 1;
}
printf("exclamationCheck = %d\n", exclamationCheck);
return 0;
}
Output:
exclamationCheck = 1
If you are looking for a laconic one liner, then you could follow #melpomene's approach:
int exclamationCheck = strchr(str, '!') != NULL;
If you are not allowed to use methods from the C String Library, then, as #SomeProgrammerDude suggested, you could simply iterate over the string, and if any character is the exclamation mark, as demonstrated in this example:
#include <stdio.h>
int main(void)
{
char str[] = "Hi, I'm odd";
int exclamationCheck = 0;
for(int i = 0; str[i] != '\0'; ++i)
{
if(str[i] == '!')
{
exclamationCheck = 1;
break;
}
}
printf("exclamationCheck = %d\n", exclamationCheck);
return 0;
}
Output:
exclamationCheck = 0
Notice that you could break the loop when at least one exclamation mark is found, so that you don't need to iterate over the whole string.
PS: What should main() return in C and C++? int, not void.
You can use plain search for ! character with
Code
#include <stdio.h>
#include <string.h>
int main(void)
{
char str[] = "Hi, I'm odd!";
int exclamationCheck = 0;
int i=0;
while (str[i]!='\0'){
if (str[i]=='!'){
exclamationCheck = 1;
break;
}
i++;
}
printf("exclamationCheck = %d\n", exclamationCheck);
return 0;
}
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.
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()
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.
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;
}
I have a problem in my C program. This is the String Search program. The problem is when I type the String aabaaacaamaad, the result comes NULL when I search for ab in it but it should not as ab is there in aabaaacaamaad. The same result also comes with am and ad which is right but why does it come with aabaaacaamaad? Code:
char* MyStrstr(char* pszSearchString, char* pszSearchWord);
int main(int argc, char* argv[])
{
char szTemp1[20] = {0};
char szTemp2[10] = {0};
char * pszTemp1 = NULL;
strcpy(szTemp1, "aabaaacaamaad");
strcpy(szTemp2, "aa");
pszTemp1 = MyStrstr(szTemp1, szTemp2);
printf("%s", pszTemp1);
getch();
return 0;
}
char* MyStrstr(char* pszSearchString, char* pszSearchWord)
{
int nFcount = 0;
int nScount = 0;
int nSearchLen = 0;
int nIndex = 0;
char* pszDelString = NULL;
if(pszSearchString == NULL || pszSearchWord == NULL) {
return NULL;
}
while(pszSearchWord[nSearchLen] != '\0') {
nSearchLen++;
}
if(nSearchLen <= 0){
return pszSearchString;
}
for(nFcount = 0; pszSearchString[nFcount] != '\0'; nFcount++) {
if(pszSearchString[nFcount] == pszSearchWord[nScount]) {
nScount++;
} else {
nScount = 0;
}
if(nScount == nSearchLen) {
nIndex = (nFcount - nScount) + 1;
pszDelString = pszSearchString + nIndex;
return pszDelString;
}
}
return NULL;
}
I see what your code is trying to do, you want to avoid a loop in a loop but however you're missing one thing. When a match fails you're not going back but still moving forward in pszSearchString while you should not. The result of this flaw is that with incomplete matches you skip characters. That's the reason why the strstr function originally uses a loop in a loop so for every character in pszSearchString there is an new loop to match with pszSearchWord. Here the original strstr.c file from BSD/Darwin:
char * strstr(const char *in, const char *str)
{
char c;
size_t len;
c = *str++;
if (!c)
return (char *) in; // Trivial empty string case
len = strlen(str);
do {
char sc;
do {
sc = *in++;
if (!sc)
return (char *) 0;
} while (sc != c);
} while (strncmp(in, str, len) != 0);
return (char *) (in - 1);
}
Is there a better of parsing the below string instead of doing a strtok() to get each field.
"subject=what&cc=bose#yahoo.com&server=smtp.yahoo.com:8000"
Basically I want to retrieve the value for each field into another char buf's.
Here is my code. Just wanted to know if there is any other better way of doing it (any better string parsing algos)
#include <stdio.h>
#include <stdint.h>
#include <string.h>
#include <stdlib.h>
#define SUBJECT "subject="
#define CC_LIST "cc="
#define SERVER "server="
static void
get_value (const char *tok, char **rval_buf, size_t field_len)
{
size_t val_size = 0;
if (!tok || !rval_buf)
return;
val_size = strlen(tok + field_len) + 1;
*rval_buf = calloc(1, val_size);
if (*rval_buf) {
strlcpy(*rval_buf, tok + field_len, val_size);
}
}
int
main (int argc, char **argv)
{
/* hard coded buf for testing */
char buf[] = "subject=what&cc=bose#yahoo.com&server=smtp.yahoo.com:8000";
char *subject_text = NULL;
char *cc_list = NULL;
char *server_addr = NULL;
char *tok = NULL;
int field_len = 0;
int val_len = 0;
tok = strtok(buf, "&");
while(tok) {
/*
* Handle the token
*/
/* check if it is subject */
if (strstr(tok, SUBJECT)) {
get_value(tok, &subject_text, strlen(SUBJECT));
} else if (strstr(tok, CC_LIST)) { /* check if it is CC */
get_value(tok, &cc_list, strlen(CC_LIST));
} else if (strstr(tok, SERVER)) { /* check if it is server */
get_value(tok, &server_addr, strlen(SERVER));
}
tok = strtok(NULL, "&");
}
/* dump data */
fprintf(stdout, "\nSUBJECT: \"%s\"\nCC_LIST: \"%s\"\nSERVER: \"%s\" \n\n",
subject_text, cc_list, server_addr);
return EXIT_SUCCESS;
}
strstr searches for one string ("the needle") inside another ("the haystack"), but you really only want to know whether the needle is the beginning of the haystack.
Here's a small suggestion: (requires #include <stdbool> or change the booleans to ints. I like bools.)
static bool
getval(const char* haystack, const char** res, const char* needle, size_t len) {
if (haystack && 0 == strncmp(haystack, needle, len)) {
*res = strdup(haystack + len);
return true;
}
return false;
}
and later:
for (tok = strtok(buf, "&"); tok; tok = strtok(NULL, "&")) {
getval(tok, &subject_text, SUBJECT, strlen(SUBJECT)) ||
getval(tok, &cc_list, CC_LIST, strlen(CC_LIST)) ||
getval(tok, &server_addr, SERVER, strlen(SERVER));
}
You can actually get away with doing the strlen inside of getval, which cuts down a lot on the noise, because most modern compilers are clever enough to inline getval and constant-fold the length of a constant string.
Use strtok()
char *strtok(char *str, const char *delim)
You can put '&' as a delimeter
I wrote a quick-n-dirty splitter for you:
int split(char* input, char delim, char*** parts)
{
int count = 1;
char** result;
char* t = input;
while(*t != '\0')
{
if (*t++ == delim)
{
count++;
}
}
result = (char**)malloc(count * sizeof(char*));
t = input;
int i = 0;
result[i] = input;
while(*t != '\0')
{
if (*t == delim)
{
*t = '\0';
result[++i] = ++t;
}
else
{
t++;
}
}
*parts = result;
return count;
}
int main()
{
char raw[] = "subject=\"some text\"&cc=abcd&server=acd.com";
char* str = _strdup(raw);
char** parts;
char** keyval;
int cnt = split(str, '&', &parts);
for(int i=0; i<cnt; ++i)
{
split(parts[i], '=', &keyval);
printf("[%d]: %s <--> %s\n", i, keyval[0], keyval[1]);
free(keyval);
}
free(parts);
getchar();
return 0;
}
Output
[0]: subject <--> "some text"
[1]: cc <--> abcd
[2]: server <--> acd.com