How to convert my malloc + strcpy to strdup in C?

Question

I am trying to save csv data in an array for use in other functions. I understand that strdup is good for this, but am unsure how to make it work for my situation. Any help is appreciated!

The data is stored in a struct:

typedef struct current{
    char **data;
}CurrentData;

Function call:

int main(void){
    int totalProducts = 0;
    CurrentData *AllCurrentData = { '\0' };
    FILE *current = fopen("C:\\User\\myfile.csv", "r");

    if (current == NULL){
        puts("current file data not found");
    }
    else{
        totalProducts = getCurrentData(current, &AllCurrentData);
    }
 fclose(current);
 return 0;
 }

How I allocated memory;

 int getCurrentData(FILE *current, CurrentData **AllCurrentData){

*AllCurrentData = malloc(totalProducts * sizeof(CurrentData));

    /*allocate struct data memory*/
    while ((next = fgetc(current)) != EOF){                                                 
        if (next == '\n'){
            (*AllCurrentData)[newLineCount].data = malloc(colCount * sizeof(char*));
            newLineCount++;
        }
    }
    newLineCount = 0;
    rewind(current);

    while ((next = fgetc(current)) != EOF && newLineCount <= totalProducts){                    

        if (ch != '\0'){
            buffer[i] = ch;
            i++;
            characterCount++;
        }

        if (ch == ',' && next != ' ' || ch == '\n' && ch != EOF){
            if (i > 0){
                buffer[i - 1] = '\0';
            }
            length = strlen(buffer);
            /*(*AllCurrentData)[newLineCount].data[tabCount] = malloc(length +  1);     /* originally was using strcpy */
            strcpy((*AllCurrentData)[newLineCount].data[tabCount], buffer);
            */
            (*AllCurrentData)[newLineCount].data[tabCount] = strdup(buffer);  /* something like this? */

            i = 0;
            tabCount++;

            for (j = 0; j < BUFFER_SIZE; j++){
                buffer[j] = '\0';
            }
        }

Answer 1

You define a ptr AllCurrentData but you should set it to NULL.

CurrentData* AllCurrentData = NULL;

In getCurrentData you use totalProducts which seems a bit odd since it is a local variable in main(), either you have another global variable with the same name or there is an error.

The **data inside the structure seems odd, instead maybe you want to parse the csv line and create proper members for them. You already have an array of CurrentData so it seems odd to have another array inside the struct -- i am just guessing cause you haven't explained that part.

Since a csv file is line based use fgets() to read one line from the file, then parse the string by using e.g. strtok or just by checking the buffer after delimiters. Here strdup can come into play, when you have taken out a token, do a strdup on it and store it in your structure.

char line[255];
if ( fgets(line,sizeof(line),current) != NULL )
{
  char* token = strdup(strtok( line, "," ));
  ...
}

Instead of allocating a big buffer that may be enough (or not) use realloc to increase your buffer as you read from the file.

That said there are faster ways to extract data from a csv-file e.g. you can read in the whole file with fread, then look for delimiters and set these to \0 and create an array of char pointers into the buffer.

Answer 2

Okay, I wouldn't comment on other parts of your code, but you can use strdup to get rid of this line (*AllCurrentData)[newLineCount].data = malloc(colCount * sizeof(char*));, and this line (*AllCurrentData)[newLineCount].data[tabCount] = strdup(buffer); /* something like this? */ and replace them with this: (*AllCurrentData)[newLineCount].data = strdup(buffer);

Answer 3

For the function to read in the array of strings I would start with the following approach. This has not been tested or even compiled however it is a starting place.

There are a number of issues not addressed by this sample. The temporary buffer size of 4K characters may or may not be sufficiently large for all lines in the file. There may be more lines of text in the file than elements in the array of pointers and there is no indication from the function that this has happened.

Improvements to this would be better error handling. Also it might be modified so that the array of pointers is allocated in the function with some large amount and then if there are more lines in the file than array elements, using the realloc() function to enlarge the array of pointers by some size. Perhaps also a check on the file size and using an average text line length would be appropriate to provide an initial size for the array of pointers.

// Read lines of text from a text file returning the number of lines.
// The caller will provide an array of char pointers which will be used
// to return the list of lines of text from the file.
int GetTextLines (FILE *hFile, char **pStringArrays, int nArrayLength)
{
    int  iBuffSize = 4096;
    int  iLineCount = 0;
    char tempBuffer [4096];

    while (fgets (tempBuffer, iBuffSize, hFile) && iLineCount < nArrayLength) {
        pStringArrays[iLineCount] = malloc ((strlen(tempBuffer) + 1) * sizeof (char));
        if (! pStringArrays[iLineCount])
            break;
        strcpy (pStringArrays[iLineCount], tempBuffer);
        iLineCount++; 
    }
    return iLineCount;
}