[文件操作]替换文件中的字符串

文件操作函数：

• int fseek(FILE *stream, long offset, int origin);

stream为文件指针

offset表示偏移量，正数表示正向偏移，负数表示负向偏移

origin文件从哪个位置开始偏移，可取值为SEEK_CUR, SEEK_END, SEEK_SET, 分别代表当前位置、文件结尾、文件开头。

• long ftell(FILE *stream);

当前文件位置指针相对于文件头的偏移字节数，使用fseek函数后，再调用ftell可以精确获取文件当前位置

• size_t fread(void *buffer, size_t size, size_t count, FILE *stream);

从文件流中读取数据count个项，每个项为size个字节，成功则返回读取到项的个数(<=count)，不成功或者读到文件末尾则返回0

• fwrite
• fputs/fputc/fputchar
• fopen
• fclose

// BambooStrReplace.cpp : Defines the entry point for the console application.
//

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

#define BUFFER_SIZE    2048            //4096=4k

char *path = "C:\...\Makefile";

const char *referStr = "ld_ar.mk";

char srcStr[BUFFER_SIZE];
char dstStr[BUFFER_SIZE];

int main()
{
    FILE *fp;
    int ret;

    // open file
    fp = fopen(path, "rb+");
    if (fp == NULL)
    {
        printf("file open failed
");
        return 0;
    }
    // goto file end
    fseek(fp, 0, SEEK_END);
    // back to 1kbytes
    if (ftell(fp) > BUFFER_SIZE)
    {
        fseek(fp, -BUFFER_SIZE, SEEK_CUR);
    }
    else
    {
        fseek(fp, -ftell(fp), SEEK_CUR);
    }
    int filePosition = ftell(fp);
    //  clear str
    memset(srcStr, 0, sizeof(srcStr));
    memset(dstStr, 0, sizeof(srcStr));

    // read file to array
    ret = fread(srcStr, 1, BUFFER_SIZE, fp);
    memcpy(dstStr, srcStr, ret);
    // get ld_ar.mk position
    char * dstPosition = strstr(srcStr, referStr);
    int SecondOffset = (int)dstPosition - (int)srcStr;
    // get " position
    while (*dstPosition != '"')
    {
        dstPosition--;
    }
    int fisrtOffset = (int)dstPosition - (int)srcStr;
    int deleteLen = SecondOffset - fisrtOffset;

    dstStr[fisrtOffset + 1] = '.';                        // add "."
    dstStr[fisrtOffset + 2] = '\';                        

    // delete string                                                                                                                
    for (int i = fisrtOffset; i < ret - deleteLen; i++)
    {
        dstStr[i+3] = srcStr[i + deleteLen];
    }
    for (int i = ret - deleteLen; i < ret; i++)
    {
        dstStr[i] = '';
    }
    // put into Makefile
    fseek(fp, filePosition, SEEK_SET);
    fputs(dstStr, fp);
    fclose(fp);
    //system("pause");
    return 0;
}