User input function C

Hi all! I've got a problem with reading user input from a console. I am trying to implement function that reads and allocates memory from the console in chunks.

First issue

First issue is I am getting some artifacts at the beginning of the output. For an input:

Sample input 1

Sample input 2

Sample input 3

Sample input 123

I get:

­_←Sample input 1

_♂Sample input 2

_|Sample input 3

_ľSample input 123

In debugger char buffer[block_size]; variable looks fine, after fgets(buffer, block_size, stdin) != NULL is executed. and I think that problem occurs in strcat(input, buffer);. I have no idea why it does that. My guess I am allocating/reallocating memory wrong.

Second issue

Second issue is that console outputs maximum of 4091 characters on Windows, with artifacts at the beginning. I have tried inputs like 5000 or 8000 'a' characters.

Is it possible to increase the input without overcomplicating my code?

Additional information

I'm using Windows 10 Pro, Version: 10.0.19044 Build 19044.

Clion IDE.

MinGW toolset.

C11 standard.

On Linux Mint machine I do not get artifacts and the console output is 4096 characters.

I do not get any errors.

Code

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

char *user_input();

int main() {


    char *x = user_input();

    printf("%s", x);
    
    return 0;
}

char *user_input() {

    const int block_size = 200;
    size_t temp_str_size, general_str_size = 0;
    char buffer[block_size];

    //allocates memory
    char *input = malloc(block_size * sizeof(char));

    do {

        //reads input to buffer
        if (fgets(buffer, block_size, stdin) != NULL) {


            temp_str_size = strlen(buffer);

            //reallocates whatever memory is needed for input 
            realloc(input, temp_str_size   general_str_size);
            
            //null check
            if (input == NULL) {
                printf("Unable to reallocate memory\n");
                return NULL;
            }
            
            
            strcat(input, buffer); // probably problem occurs here 

            // increases general string size for expanding memory reallocation
            general_str_size  = temp_str_size;
        } else {
            return NULL;
        }
        
        
    } while (temp_str_size == block_size - 1);
    return input;
}

CodePudding user response：

strcat(input, buffer) both params need to contain strings. input content is unintialised and hence has indeterminate values. Initialise with input[0] = '\0' after malloc.