Question

可能重复：
How do you determine the size of a file in C?

如何找出用C编写的应用程序打开的文件大小？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，我使用malloc()分配。只写malloc(10000*sizeof(char));是恕我直言，这是一个坏主意。

Answer 1

您需要寻找文件的末尾，然后询问职位：

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

然后你可以回头，例如：

fseek(fp, 0L, SEEK_SET);

或（如果想要开始）

rewind(fp);

Answer 2

使用标准库：

假设您的实施有意义地支持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

的Linux / POSIX：

您可以使用stat（如果您知道文件名）或fstat（如果您有文件描述符）。

以下是stat的示例：

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

的Win32：

您可以使用GetFileSize或GetFileSizeEx。

Answer 3

如果您有文件描述符fstat()，则返回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;

Answer 4

我最后只做了一个简短而甜蜜的fsize函数（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愚蠢，但我可以看出为什么它很难，因为并非每个“文件”都有一个大小（例如/dev/null）

Answer 5

您是否考虑过不计算文件大小，只是在必要时增加数组？这是一个例子（省略错误检查）：

#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;
}

这样做的优点是即使对于无法获取文件大小的流（如stdin）也可以工作。

Answer 6

如果您使用的是Linux，请认真考虑使用glib中的g_file_get_contents函数。它处理所有加载文件，分配内存和处理错误的代码。

Answer 7

如何使用 lseek / fseek / stat < / strong> / fstat 来获取文件大小？

#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 == (long)-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 == (off_t)-1) { printf("failed to lseek %s\n", filename); exit(EXIT_FAILURE); } printf("[*] seek_filesize - file: %s, size: %lld\n", filename, 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; }

Answer 8

#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;
}

HTH

如何在C中获取文件大小？

8 个答案:

使用标准库：

的Linux / POSIX：

的Win32：