文件频繁读写优化函数

今天药忘吃喽~ 2022-05-25 09:18 128阅读 0赞

频繁的io读写容易降低程序的效率，避免的此类情况的核心思路是减少io次数，从io中读取足够长度的数据缓存到缓冲区，从缓冲区读取。

#include <stdio.h>
    #include <string.h>
    #include <stdlib.h>
    
    #define PPS_BUFFER_FILE_NAME_LEN 128
    
    typedef struct file_buffer_t {
        char file_name[128];
        char *buffer;
        int buffer_size;
        int buffer_len;
        int file_start_pos;
        int file_end;
        int offset;
    } FILE_BUF;
    
    
    FILE_BUF *pps_buf_init(char *file_name, int buffer_size)
    {
        FILE_BUF *p = NULL;
        int file_name_len = 0;
    
        file_name_len = strlen(file_name);
        if (file_name == NULL || file_name_len == 0 || buffer_size <= 0) {
            printf("invalid parameters!\n");
            return NULL;
        }
    
        p = calloc(sizeof(FILE_BUF), 1);
        if (p == NULL) {
            printf("Apply struct memory failed!\n");
            return NULL;
        }
    
        if (file_name_len > PPS_BUFFER_FILE_NAME_LEN) {
            printf("buffer file name can't exceed %d\n", PPS_BUFFER_FILE_NAME_LEN);
            free(p);
            return NULL;
        }
    
        strncpy(p->file_name, file_name, file_name_len);
        p->buffer_size = buffer_size;
    
        p->buffer = calloc(buffer_size, 1);
        if (p->buffer == NULL) {
            printf("Apply buffer memory failed!\n");
            free(p);
            return NULL;
        }
        return p;
    }
    
    int pps_buf_deinit(FILE_BUF *fbp)
    {
    
        if (fbp == NULL)
            return -1;
    
        if (fbp->buffer != NULL) {
            free(fbp->buffer);
            fbp->buffer = NULL;
        }
    
        free(fbp);
        return 0;
    }
    
    int pps_buf_read(char *buf, int size, int count, FILE_BUF *fbp)
    {
        int ret = -1, readlen = 0;
    
        if (fbp == NULL || fbp->buffer == NULL) {
            printf("error FILE_BUF pointer, pelease init first!\n");
            return -1;
        }
    
        readlen = size * count;
        if (readlen > fbp->buffer_size) {
            printf("read len can't exceed buffer size!\n");
            return -1;
        }
    
        if (fbp->file_end && fbp->offset == fbp->buffer_len)
            return -1;
    
        if (fbp->buffer_len == 0 || fbp->offset + readlen > fbp->buffer_size) {
            FILE *fp = NULL;
            fp = fopen(fbp->file_name, "r");
            if (fp == NULL) {
                printf("open file [%s] failed", fbp->file_name);
                return -1;
            } else {
                printf("open and read file %s\n", fbp->file_name);
            }
    
            ret = fseek(fp, fbp->file_start_pos + fbp->offset , SEEK_SET);
            if (ret) {
                printf("seek file pos filed!\n");
                fclose(fp);
                return -1;
            }
            ret = fread(fbp->buffer, 1, fbp->buffer_size, fp);
            if (ret != fbp->buffer_size) {
                if (feof(fp)) {
                    fbp->file_start_pos = fbp->file_start_pos + fbp->offset;
                    fbp->offset = 0;
                    fbp->buffer_len = ret;
                    fbp->file_end = 1;
                } else {
                    printf("read file [%s] filed!\n", fbp->file_name);
                    fclose(fp);
                    return -1;
                } 
            } else {
                fbp->file_start_pos = fbp->file_start_pos + fbp->offset;
                fbp->offset = 0;
                fbp->buffer_len = ret;
            }
            fclose(fp);
        }
    
        if (fbp->offset + readlen > fbp->buffer_len) {
            readlen = fbp->buffer_len - fbp->offset;
        }
        memcpy(buf, fbp->buffer + fbp->offset, readlen);
        fbp->offset += readlen;
        return readlen;
    }
    
    int main(int argc, char *argv[])
    {
        int ret = -1;
        FILE_BUF *fbp = NULL;
        char str[256];
    
        fbp = pps_buf_init("data.txt", 32*1024);
        if (fbp == NULL) {
            printf("error init\n");
            return -1;
        }
        while (pps_buf_read(str, 1, 128, fbp) != -1) {
            printf("[ %s ]\n", str);
        }
    
        pps_buf_deinit(fbp);
        printf("Hello World!\n");
    
        return 0;
    }