如何解析不能完全适合内存RAM的文件

我已经创建了一个框架来解析合适大小的文本文件,这些文件可以放在内存RAM中,而且现在情况还顺利.我没有抱怨,但是如果遇到我必须处理大文件的情况,比如大于8GB(这是我的大小)怎么办？
处理这些大文件的有效方法是什么？

我的框架：

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

int Parse(const char *filename,const char *outputfile);

int main(void)
{
    clock_t t1 = clock();
    /* ............................................................................................................................. */
    Parse("file.txt",NULL);
    /* ............................................................................................................................. */
    clock_t t2 = clock();
    fprintf(stderr,"time elapsed: %.4f\n",(double)(t2 - t1) / CLOCKS_PER_SEC);
    fprintf(stderr,"Press any key to continue . . . ");
    getchar();
    return 0;
}

long GetFileSize(FILE * fp)
{
    long f_size;
    fseek(fp,0L,SEEK_END);
    f_size = ftell(fp);
    fseek(fp,SEEK_SET);
    return f_size;
}

char *dump_file_to_array(FILE *fp,size_t f_size)
{
    char *buf = (char *)calloc(f_size + 1,1);
    if (buf) {
        size_t n = 0;
        while (fgets(buf + n,INT_MAX,fp)) {
            n += strlen(buf + n);
        }
    }
    return buf;
}

int Parse(const char *filename,const char *outputfile)
{
    /* open file for reading in text mode */
    FILE *fp = fopen(filename,"r");
    if (!fp) {
        perror(filename);
        return 1;
    }
    /* store file in dynamic memory and close file */
    size_t f_size = GetFileSize(fp);
    char *buf = dump_file_to_array(fp,f_size);
    fclose(fp);
    if (!buf) {
        fputs("error: memory allocation Failed.\n",stderr);
        return 2;
    }
    /* state machine variables */
    // ........

    /* array index variables */
    size_t x = 0;
    size_t y = 0;
    /* main loop */
    while (buf[x]) {
        switch (buf[x]) {
            /* ... */
        }
        x++;
    }
    /* NUL-terminate array at y */
    buf[y] = '\0';
    /* write buffer to file and clean up */
    outputfile ? fp = fopen(outputfile,"w") :
                 fp = fopen(filename,"w");
    if (!fp) {
        outputfile ? perror(outputfile) :
                     perror(filename);
    }
    else {
        fputs(buf,fp);
        fclose(fp);
    }
    free(buf);
    return 0;
}

基于框架的模式删除功能：

int delete_pattern_in_file(const char *filename,const char *pattern,"r");
    if (!fp) {
        perror(filename);
        return 1;
    }
    /* copy file contents to buffer and close file */
    size_t f_size = GetFileSize(fp);
    char *buf = dump_file_to_array(fp,f_size);
    fclose(fp);
    if (!buf) {
        fputs("error - memory allocation Failed",stderr);
        return 2;
    }
    /* delete first match */
    size_t n = 0,pattern_len = strlen(pattern);
    char *tmp,*ptr = strstr(buf,pattern);
    if (!ptr) {
        fputs("No match found.\n",stderr);
        free(buf);
        return -1;
    }
    else {
        n = ptr - buf;
        ptr += pattern_len;
        tmp = ptr;
    }
    /* delete the rest */
    while (ptr = strstr(ptr,pattern)) {
        while (tmp < ptr) {
            buf[n++] = *tmp++;
        }
        ptr += pattern_len;
        tmp = ptr;
    }
    /* copy the rest of the buffer */
    strcpy(buf + n,tmp);
    /* open file for writing and print the processed buffer to it */
    outputfile ? fp = fopen(outputfile,fp);
        fclose(fp);
    }
    free(buf);
    return 0;
}

解决方法

如果您希望坚持使用当前的设计,可以选择mmap()文件,而不是将其读入内存缓冲区.

您可以将函数dump_file_to_array更改为以下(特定于Linux)：

char *dump_file_to_array(FILE *fp,size_t f_size) {
   buf = mmap(NULL,f_size,PROT_READ,MAP_SHARED,fileno(fp),0);
   if (buf == MAP_Failed)
       return NULL;
   return buf;
}

现在你可以读取文件,内存管理器会自动关注只保存内存中相关的文件部分.对于Windows,存在类似的机制.

原文地址：https://www.jb51.cc/c/119874.html