利用C语言对文件进行字符串的替换

#include<stdio.h>
#include<errno.h>
#include<unistd.h>
#include<stdlib.h>
#include<string.h>
#include<sys/stat.h>
#define LINE_SIZE 256
/*********
 * 函数名：Subit
 * 功能：将pathname文件中的字符串s1替换成s2
 * 参数：
 *      @s1:被替换字符串
 *      @s2:替换字符串
 *      @pathname:文件名
 * 返回值：
 *      无
 * *******/
void Subtit(const char*s1,const char *s2,const char *pathname)
{

    int len_s1 = strlen(s1);
    int len_s2 = strlen(s2);
    FILE *fileline=fopen(pathname,"r+");

    if(fileline==NULL)
    {
        printf("Fopen %s error!",pathname);
        exit(0);
    }
    struct stat filestate;
    stat(pathname,&filestate);
    char *filebuffer=(char *)malloc(sizeof(char)*(filestate.st_size+1));
    for (int i = 0,ch=0;ch!=EOF;i++)
    {
        ch = fgetc(fileline);
        filebuffer[i]=ch;
    }  
    fseek(fileline,0,SEEK_SET);    
    for (char *index_1 = filebuffer,*index_2 = filebuffer;;)
    {
        index_2 = strstr(index_1,s1);
        if(index_2)
        {
            for(int i=0;i<index_2-index_1;i++)
            {
                fputc(index_1[i],fileline);
            }
            for(int i=0;i<len_s2;i++)
            {
                fputc(s2[i],fileline);
            }
            index_1=index_2+len_s1;
        }
        else
        {
            while(*index_1!=EOF)
            {
                fputc(*index_1++,fileline);
            }
            break;
        }
    }
    free(filebuffer);
    fclose(fileline);
}
void usage()
{
    printf("================Usage================\n");
    printf("./a.out [string1] [string2] [filename]\n");
    printf("Tips:Replace string1 with string2!\n");
    printf("=====================================\n");
}
int main(int argc,char **argv)
{
    if(argc!=4)
    {
        usage();
        printf("The parameters are error!\n");
        return -1;
    }
    Subtit(argv[1],argv[2],argv[3]);
    printf("Successful replacement\n");
    return 0;
}