424

如何找出用 C 编写的应用程序打开的文件的大小？我想知道大小，因为我想将加载文件的内容放入一个字符串中，我使用malloc(). 只是写作malloc(10000*sizeof(char));是恕我直言一个坏主意。

4

8 回答 8

584

您需要寻找到文件的末尾，然后询问位置：

fseek(fp, 0L, SEEK_END);
sz = ftell(fp);

然后您可以回溯，例如：

fseek(fp, 0L, SEEK_SET);

或（如果想从头开始）

rewind(fp);
于 2008-10-26T20:57:29.897 回答
410

使用标准库：

假设您的实现有意义地支持 SEEK_END：

fseek(f, 0, SEEK_END); // seek to end of file
size = ftell(f); // get current file pointer
fseek(f, 0, SEEK_SET); // seek back to beginning of file
// proceed with allocating memory and reading the file

Linux/POSIX：

您可以使用stat（如果您知道文件名），或者fstat（如果您有文件描述符）。

下面是一个统计示例：

#include <sys/stat.h>
struct stat st;
stat(filename, &st);
size = st.st_size;

赢32：

您可以使用GetFileSize或GetFileSizeEx。

于 2008-10-26T20:59:32.153 回答
120

如果您有文件描述符，则fstat()返回一个包含文件大小的统计结构。

#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>

// fd = fileno(f); //if you have a stream (e.g. from fopen), not a file descriptor.
struct stat buf;
fstat(fd, &buf);
off_t size = buf.st_size;
于 2008-10-26T21:17:18.017 回答
22

我最终只是做了一个简短而甜蜜的fsize功能（注意，没有错误检查）

int fsize(FILE *fp){
    int prev=ftell(fp);
    fseek(fp, 0L, SEEK_END);
    int sz=ftell(fp);
    fseek(fp,prev,SEEK_SET); //go back to where we were
    return sz;
}

标准 C 库没有这样的功能有点傻，但我明白为什么它会很困难，因为不是每个“文件”都有大小（例如/dev/null）

于 2011-03-27T02:09:48.093 回答
17

如何使用lseek / fseek / stat / fstat获取文件大小？

#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/stat.h>

void
fseek_filesize(const char *filename)
{
    FILE *fp = NULL;
    long off;

    fp = fopen(filename, "r");
    if (fp == NULL)
    {
        printf("failed to fopen %s\n", filename);
        exit(EXIT_FAILURE);
    }

    if (fseek(fp, 0, SEEK_END) == -1)
    {
        printf("failed to fseek %s\n", filename);
        exit(EXIT_FAILURE);
    }

    off = ftell(fp);
    if (off == -1)
    {
        printf("failed to ftell %s\n", filename);
        exit(EXIT_FAILURE);
    }

    printf("[*] fseek_filesize - file: %s, size: %ld\n", filename, off);

    if (fclose(fp) != 0)
    {
        printf("failed to fclose %s\n", filename);
        exit(EXIT_FAILURE);
    }
}

void
fstat_filesize(const char *filename)
{
    int fd;
    struct stat statbuf;

    fd = open(filename, O_RDONLY, S_IRUSR | S_IRGRP);
    if (fd == -1)
    {
        printf("failed to open %s\n", filename);
        exit(EXIT_FAILURE);
    }

    if (fstat(fd, &statbuf) == -1)
    {
        printf("failed to fstat %s\n", filename);
        exit(EXIT_FAILURE);
    }

    printf("[*] fstat_filesize - file: %s, size: %lld\n", filename, statbuf.st_size);

    if (close(fd) == -1)
    {
        printf("failed to fclose %s\n", filename);
        exit(EXIT_FAILURE);
    }
}

void
stat_filesize(const char *filename)
{
    struct stat statbuf;

    if (stat(filename, &statbuf) == -1)
    {
        printf("failed to stat %s\n", filename);
        exit(EXIT_FAILURE);
    }

    printf("[*] stat_filesize - file: %s, size: %lld\n", filename, statbuf.st_size);

}

void
seek_filesize(const char *filename)
{
    int fd;
    off_t off;

    if (filename == NULL)
    {
        printf("invalid filename\n");
        exit(EXIT_FAILURE);
    }

    fd = open(filename, O_RDONLY, S_IRUSR | S_IRGRP);
    if (fd == -1)
    {
        printf("failed to open %s\n", filename);
        exit(EXIT_FAILURE);
    }

    off = lseek(fd, 0, SEEK_END);
    if (off == -1)
    {
        printf("failed to lseek %s\n", filename);
        exit(EXIT_FAILURE);
    }

    printf("[*] seek_filesize - file: %s, size: %lld\n", filename, (long long) off);

    if (close(fd) == -1)
    {
        printf("failed to close %s\n", filename);
        exit(EXIT_FAILURE);
    }
}

int
main(int argc, const char *argv[])
{
    int i;

    if (argc < 2)
    {
        printf("%s <file1> <file2>...\n", argv[0]);
        exit(0);
    }

    for(i = 1; i < argc; i++)
    {
        seek_filesize(argv[i]);
        stat_filesize(argv[i]);
        fstat_filesize(argv[i]);
        fseek_filesize(argv[i]);
    }

    return 0;
}
于 2010-01-05T02:36:01.360 回答
9

您是否考虑过不计算文件大小而只在必要时增加数组？这是一个示例（省略了错误检查）：

#define CHUNK 1024

/* Read the contents of a file into a buffer.  Return the size of the file 
 * and set buf to point to a buffer allocated with malloc that contains  
 * the file contents.
 */
int read_file(FILE *fp, char **buf) 
{
  int n, np;
  char *b, *b2;

  n = CHUNK;
  np = n;
  b = malloc(sizeof(char)*n);
  while ((r = fread(b, sizeof(char), CHUNK, fp)) > 0) {
    n += r;
    if (np - n < CHUNK) { 
      np *= 2;                      // buffer is too small, the next read could overflow!
      b2 = malloc(np*sizeof(char));
      memcpy(b2, b, n * sizeof(char));
      free(b);
      b = b2;
    }
  }
  *buf = b;
  return n;
}

即使对于无法获得文件大小的流（如标准输入），这也具有工作的优势。

于 2009-10-29T13:38:45.027 回答
8

如果您使用的是 Linux，请认真考虑只使用 glib 中的g_file_get_contents函数。它处理加载文件、分配内存和处理错误的所有代码。

于 2008-10-26T21:13:54.043 回答
-42 
#include <stdio.h>

#define MAXNUMBER 1024

int main()
{
    int i;
    char a[MAXNUMBER];

    FILE *fp = popen("du -b  /bin/bash", "r");

    while((a[i++] = getc(fp))!= 9)
        ;

    a[i] ='\0';

    printf(" a is %s\n", a);

    pclose(fp);
    return 0;
}

高温高压

于 2008-10-29T13:50:48.337 回答