Returning a pointer from a function just isn't working

Happy Labor Day Weekend. I've got a pointer question that I haven't been able to resolve. I'm trying to pass a string to a function which removes "mdata," from the beginning of the string and then returns a pointer to the new string. It ain't werkin... :( I'm not defining my pointer variables correctly or something.

Code:

---

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


char *rmDataForDBmarker(char *stringToClean, char *whatToRemove);


int main()
{
    char logToKeep[] = "mdata,";                                // this is the key word of the log entry to keep
    char *logFinder = "mdata,b1a571,3324 d,123.46,987.99";
    char *dataMarkerRmvd;


    printf("\n string before the function: %s", logFinder);
    dataMarkerRmvd = rmDataForDBmarker(logFinder, logToKeep);
    printf("\n back from rmDataForDBmarker(): dataMarkerRmvd = %s", dataMarkerRmvd);
}


char *rmDataForDBmarker(char *stringToClean, char *whatToRemove){ // in this case
    printf("\n Now the code is in the function...");
    printf("\n The next stringToClean is = %s", stringToClean);
    int i, j = 0, k = 0,n = 0;
    int flag = 0;
    char *neww[100];                        // declaring neww as a pointer


    for(i = 0 ; stringToClean[i] != '\0' ; i++)
    {
        k = i;
        while(stringToClean[i] == whatToRemove[j])
        {
            i++,j++;
            if(j == strlen(whatToRemove))
            {
                flag = 1;
                break;
            }
        }
    j = 0;
    if(flag == 0){
        i = k;
    }
    else{
        flag = 0;
    }
    printf("\nstringToClean[i] = %c", stringToClean[i]);
    n++;
    printf("\ni=%d  n=%d", i, n);
    neww[n] = stringToClean[i];
    printf("\n neww[n] = %c", neww[n]);
    }
    neww[n] = '\0';
    printf("\n Here's the original string: %s", stringToClean);
    printf("\n String with %s removed: %s", whatToRemove, neww);
    printf("\n The memory location of neww: %p", neww);
    return neww;                        // trying to return the pointer to neww
}

---

When I compile it, the build log provides some insight that I don't understand:

Code:

---

C:\work\arduino\trash\Untitled6.c|46|warning: assignment to 'char *' from 'char' makes pointer from integer without a cast [-Wint-conversion]|

C:\work\arduino\trash\Untitled6.c|53|warning: returning 'char **' from a function with incompatible return type 'char *' [-Wincompatible-pointer-types]|

C:\work\arduino\trash\Untitled6.c|53|warning: function returns address of local variable [-Wreturn-local-addr]|

---

I can see in the output that the string looks to be written to the "neww" string. The output looks like this:

Attachment 16492

I'm a novice coder. If someone could point me in the right direction, I'd appreciate it.

There are two main problems.
1. char *neww[100];
isn't an array of chars, nor even a simple char pointer.
It's an array of pointers.

2. You can't return a pointer to a local variable
This is your 3rd error message.

The usual means of getting a string result is to pass in the output string pointer as a parameter, like so.

Code:

---

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

void rmDataForDBmarker(char *stringToClean, char *whatToRemove, char *answer);
 
int main()
{
    char logToKeep[] = "mdata,";                                // this is the key word of the log entry to keep
    char *logFinder = "mdata,b1a571,3324 d,123.46,987.99";
    char dataMarkerRmvd[100] = {};

    printf("string before the function: %s\n", logFinder);
    rmDataForDBmarker(logFinder, logToKeep, dataMarkerRmvd);
    printf("back from rmDataForDBmarker(): dataMarkerRmvd = %s\n", dataMarkerRmvd);
}
 
void rmDataForDBmarker(char *stringToClean, char *whatToRemove, char *answer){ // in this case
    printf("Now the code is in the function...\n");
    printf("The next stringToClean is = %s\n", stringToClean);
    char *p = strstr(stringToClean, whatToRemove);
    if ( p ) {
        p += strlen(whatToRemove);  // get to the end of the marker
        strcpy(answer,p);          // copy to the answer
    }
}

---

Code:

---

$ gcc foo.c
$ ./a.out
string before the function: mdata,b1a571,3324 d,123.46,987.99
Now the code is in the function...
The next stringToClean is = mdata,b1a571,3324 d,123.46,987.99
back from rmDataForDBmarker(): dataMarkerRmvd = b1a571,3324 d,123.46,987.99

---

It's usual for the newlines to be at the end of printf strings, not at the beginning.

Hey Salem, Thank you for responding. I've reworked my actual source (162 lines) to use the code you provided. I'm amazed at how you took the crazy loop that I had to remove the beginning characters with something much easier to comprehend.

To incorporate your code into slightly large program, I added some code just after your line:

Code:

---

strcpy(answer,p);          // copy to the answer

---

I added:

Code:

---

        // insert write to disk
        printf("\n answer = %s", answer);
        FILE *fileDst = fopen("entriesForDBimport.txt", "w");
        if (fileDst == NULL){
            printf("\nUnable to open the file to write to.");
            exit(1);
        }
        else {
            fputs(answer, fileDst);
        }


        fclose(fileDst);
        // end added code

---

The above works great for me in a test program but, not when I make it part of my larger program which to me seems almost exactly like the function you posted for me:

Code:

---

void rmDataForDBmarker(char *stringToClean, char *whatToRemove, char *answer){ // in this case
    printf("Now the code is in the function...\n");
    printf("The next stringToClean is = %s\n", stringToClean);
    char *p = strstr(stringToClean, whatToRemove);
    if ( p ) {
        p += strlen(whatToRemove);  // get to the end of the marker
        strcpy(answer,p);          // copy to the answer
        printf("\n answer = %s", answer);


        // insert write to disk
        FILE *fileDst = fopen("entriesForDBimport.txt", "w");
        if (fileDst == NULL){
            printf("\nUnable to open the file to write to.");
            exit(1);
        }
        else {
            fputs(answer, fileDst);
        }
        fclose(fileDst);
        // end added code
    }
}

---

Here is the log on my console:
Attachment 16493
The Entry is not added to the log. Anything obviously wrong?

The writing to the file should be in the caller to rmDataForDBmarker, not in the function itself.

The ideal function is small, and does exactly one thing described by the name of the function.

FWIW, opening the file in "w" mode will lose any previous contents.

Thank you Salem for all your help!