Thread: Saving data into a array with snprintf

Hello,

I have this code which read some data from a text file. Then I save the data into a 2D array dynamically with malloc. Until codeline 57 this works fine. Then I would like to append some lines.
But at code line 59 I would like save the manipulated data into the array: char appendedLine[MAX_LINE_LENGTH], and print it.
But this does not work, and I did not know why. Can anybody help me to solve this problem?

Code:

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

#define MAX_LINE_LENGTH 300    // maximal length of a line of the input file
#define MAX_LINES 100000       // lines of input file

int main()
{


    // Read the lines from the file
        FILE *fp = fopen("input2.txt", "r");
    if (fp == NULL)
    {
        printf("Failed to open the file.\n");
        return 1;
    }

    // Allocate memory for a 2D array dynamically
    char **lines = (char **)malloc(MAX_LINES * sizeof(char *));
    if (lines == NULL)
    {
        printf("Failed to allocate memory for lines.\n");
        return 1;
    }

    for (int i = 0; i < MAX_LINES; i++)
    {
        lines[i] = (char *)malloc(MAX_LINE_LENGTH * sizeof(char));
        if (lines[i] == NULL)
        {
            printf("Failed to allocate memory for line %d.\n", i);
            return 1;
        }
    }


    int lineCount = 0;
    char line[MAX_LINE_LENGTH];

    while (fgets(line, sizeof(line), fp) != NULL)
    {
        if (line[strlen(line) - 1] == '\n')     // at the end of each line \n will be deleted
            line[strlen(line) - 1] = '\0';
        strcpy(lines[lineCount], line);
        lineCount++;
        if (lineCount >= MAX_LINES)
        {
            printf("Exceeded maximum number of lines.\n");
            break;
        }
    }

    fclose(fp);

    // Append line
    char appendedLine[MAX_LINE_LENGTH];
    snprintf(appendedLine[0], MAX_LINE_LENGTH, "%s%s%s\n", lines[3], lines[22], lines[41]);
    snprintf(appendedLine[1], MAX_LINE_LENGTH, "%s%s%s\n", lines[5], lines[24], lines[43]);
    snprintf(appendedLine[2], MAX_LINE_LENGTH, "%s%s%s\n", lines[7], lines[26], lines[45]);

    printf("%s\n", appendedLine[0]);
    printf("%s\n", appendedLine[1]);
    printf("%s\n", appendedLine[2]);
    

    // Free the dynamically allocated memory
    for(int i = 0; i < MAX_LINES; i++)
    {
        free(lines[i]);
    }
    free(lines);

    return 0;
}

Try

Code:

    char appendedLine[3][MAX_LINE_LENGTH*3+1];
    snprintf(appendedLine[0], sizeof(appendedLine[0]), "%s%s%s\n", lines[3], lines[22], lines[41]);
    snprintf(appendedLine[1], sizeof(appendedLine[1]), "%s%s%s\n", lines[5], lines[24], lines[43]);
    snprintf(appendedLine[2], sizeof(appendedLine[2]), "%s%s%s\n", lines[7], lines[26], lines[45]);

1. You need 3 of them
2. Each needs to be 3* the length of the combined strings, +1 for the newline.

> printf("%s\n", appendedLine[0]);
Or maybe you have the newline here instead.

But now you have two newlines.