Why do words break into strange symbols when decrpyting authenticated text with OpenSSL on Ubuntu?

I am working on using OpenSSL in Linux Ubuntu to perform authenticated encryption/decryption. I am currently using C for the code, AES-CTR Encryption method for ciphering the text, HMAC-SHA256 for the tag. My code works by using Makefile for command "make"; after that, using the two instructions shown below and original.txt for original text, shared.key for the key to encrypt/decrypt. My problem here is that although no error occurs(I tried to handle as many errors as possible, but there can be more…) during encryption and decryption, when I open the decryption.txt file, generated after the decrpytion, the words are broken into stange symbols…

Here is the C code that I’ve written:

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <openssl/sha.h>
#include <openssl/evp.h>
#include <openssl/hmac.h>

char* readFile(char* fileName){
    int size;
    int count;
    FILE *fp = fopen(fileName, "r");
    fseek(fp, 0, SEEK_END);
    size = ftell(fp);
    char* buffer = malloc(size+1);
    char* result = malloc(size+1);
    memset(buffer, 0, size+1);
    memset(result, 0, size+1);
    fseek(fp, 0, SEEK_SET);
    while(1){
        char* pStr = fgets(buffer, size+1, fp);
        if(pStr==NULL)break;
        strcat(result, pStr);
    }
    fclose(fp);
    free(buffer);
    return result;
}

int main(int argc, char* argv[]){

    if(argc != 10){
        printf("ERRORn");
        exit(2);
    }
    int ikey, iin, iout, itag;
    for(int i=2; i < 9;i+=2){
        if(!strcmp(argv[i], "-key")) ikey = i+1;
        else if(!strcmp(argv[i], "-in")) iin = i+1;
        else if(!strcmp(argv[i], "-out")) iout = i+1;
        else if(!strcmp(argv[i], "-tag")) itag = i+1;
    }
    if(ikey+iin+iout+itag != 24){
        printf("ERRORn");
        exit(2);
    }
    char* key = readFile(argv[ikey]);
    char *iv = "0123456789012345";



    if(!strcmp(argv[1], "enc")){
        FILE *inFp = fopen(argv[iin],"rb");
        FILE *outFp = fopen(argv[iout], "wb");
        int inLen, outLen;
        char inBuf[BUFSIZ], outBuf[BUFSIZ+EVP_MAX_BLOCK_LENGTH];
        EVP_CIPHER_CTX* ctx = EVP_CIPHER_CTX_new();
        EVP_EncryptInit_ex(ctx, EVP_aes_256_ctr(), NULL, key, iv);
        while((inLen=fread(inBuf, 1, sizeof(inBuf), inFp))>0){

            if(!EVP_EncryptUpdate(ctx, outBuf, &outLen, inBuf, inLen)){
                printf("ERRORn");
                EVP_CIPHER_CTX_cleanup(ctx);
                exit(2);
            }
            fwrite(outBuf, 1, outLen, outFp);
        }
        if(!EVP_EncryptFinal_ex(ctx, outBuf, &outLen)){
            printf("ERRORn");
            EVP_CIPHER_CTX_cleanup(ctx);
            exit(2);
        }
        fwrite(outBuf, 1, outLen, outFp);
        EVP_CIPHER_CTX_cleanup(ctx);

        fclose(inFp);
        fclose(outFp);
        char* cipher = readFile(argv[iout]);
        char* hashVal;
        hashVal = HMAC(EVP_sha256(), key,strlen((char*)key), cipher, strlen((char*)cipher), NULL, NULL);
        FILE *tagFp = fopen(argv[itag], "w");
        fwrite(hashVal, 1, strlen(hashVal), tagFp);
        exit(0);
    }
    else if(!strcmp(argv[1], "dec")){
        FILE *inFp = fopen(argv[iin],"rb");
        char* cipher = readFile(argv[iin]);
        char* hashVal;
        hashVal = HMAC(EVP_sha256(), key,strlen(key), cipher, strlen(cipher), NULL, NULL);
        char* compareVal = readFile(argv[itag]);
        if(strcmp(compareVal, hashVal) != 0){
            printf("VERIFICATION FAILUREn");
            exit(1);
        }

        FILE *outFp = fopen(argv[iout], "wb");
        int inLen, outLen;
        char inBuf[BUFSIZ], outBuf[BUFSIZ+EVP_MAX_BLOCK_LENGTH];
        EVP_CIPHER_CTX* ctx = EVP_CIPHER_CTX_new();
        EVP_DecryptInit_ex(ctx, EVP_aes_256_ctr(), NULL, key, iv);
        //printf("First Buf %sn", outBuf);
        //printf("First Buf %sn", inBuf);
        while((inLen=fread(inBuf, 1, sizeof(inBuf), inFp))>0){
            //printf("Second Buf %sn", outBuf);
            //printf("Second Buf %sn", inBuf);
            if(!EVP_DecryptUpdate(ctx, outBuf, &outLen, inBuf, inLen)){
                printf("ERRORn");
                EVP_CIPHER_CTX_cleanup(ctx);
                exit(2);
            }
            //printf("Third Buf %sn", outBuf);
            //printf("Third Buf %sn", inBuf);
            //printf("First number %dn", inLen);
            fwrite(outBuf, 1, outLen, outFp);
        }
        if(!EVP_DecryptFinal_ex(ctx, outBuf, &outLen)){
            printf("ERRORn");
            EVP_CIPHER_CTX_cleanup(ctx);
            exit(2);
        }
        fwrite(outBuf, 1, outLen, outFp);
        EVP_CIPHER_CTX_cleanup(ctx);
        fclose(inFp);
        fclose(outFp);
        exit(0);
    }
    exit(0);
}

And below is the Makefile that I have used to compile the upper code with gcc, using "make" command:

cryp: cryp.o
    gcc -o $@ cryp.o -lssl -lcrypto

cryp.o: cryp.c

For the original.txt and shared.key, I just typed a simple sentence like "This is original text" and "This is shared key".
With these elements, I used ./cryp enc -key shared.key -in original.txt -out encrypted.txt -tag encrypted.tag instruction in Linux terminal(Within the file storage that contains the elements) for encryption, and ./cryp dec -key shared.key -in encrypted.txt -tag encrypted.tag -out decrypted.txt instuction for decryption.
After these actions, I expected a decrypted.txt that contains same content as original.txt, but the generated decrypted.txt showed words that are broken into stange symbols…What can I do to fix this situation? PLEASE help…

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I fixed the code(To be specific, the readFile() function part) and it worked for me! I posted the fixed function below, but as I can declare it solved by my code after two days, I want to modify the code if there are any problems left to solve. Please help!