文件读取及比较&文件信息保存

#include <stdio.h>
#include <stdlib.h>
//#include <regex.h>
char* file_name_1 = "D:\testfile.txt";
char* file_name_2 = "D:\testfile_1.cfg";
char* file_name_3 = "D:\testfile_flag.txt";

#define ERROR -1
#define OK 0
int file_length(char* fileName)
{
    FILE* fp;
    int file_set_val,file_end_val;
    fp = fopen(fileName, "r");
    if(fp == NULL)
    {
        printf("read file fail
");
        return ERROR;
    }
    fseek(fp, 0 , SEEK_SET);
    file_set_val = ftell(fp);
    fseek(fp, 0 , SEEK_END);
    file_end_val = ftell(fp);    
    printf("file length is %d. 
file_set_val:%d file_end_val:%d 
", file_end_val-file_set_val,file_set_val, file_end_val);
    return file_end_val-file_set_val;
}


int read_file(char* fileName, char* content, int len)
{
    FILE* fp;
    fp = fopen(fileName, "r");
    if(fp == NULL)
    {
        printf("read file fail
");
        return ERROR;
    }
    fread(content, len, 1, fp);
    printf("read content is:%s
", content);
    return 0;
}

int back_para_increase(char* fileName, int flag)
{
    FILE* fp;    
    fp = fopen(fileName, "ab");
    if(fp == NULL)
    {
        printf("read file fail
");
        return ERROR;
    }
    if(flag)
    {
        fputc('1', fp);
    }    
    fclose(fp);    
}

int file_compare()
{
    char* content_1;
    char* content_2;
    int len = 0, flag_val = 0;
    
    len = file_length(file_name_1);
    content_1 = (char*)malloc(len);
    memset(content_1, 0, len);
    read_file(file_name_1, content_1, len);
    
    len = file_length(file_name_2);
    content_2 = (char*)malloc(len);
    memset(content_2, 0, len);
    read_file(file_name_2, content_2, len);
    
    if(strcmp(content_1, content_2))
    {
        back_para_increase(file_name_3,1);
        flag_val = file_length(file_name_3);
        printf("back_para_increase:%d
",flag_val);
    }
    free(content_1);
    free(content_2);
}

int main()
{
    printf("***************************
");
    file_compare();
    return 0;
}