最近不得不用c语言写个小程序(其实用shell, perl等脚本相当简单)，其中要处理一个表格文件。这个文件的信息就是一张表，例如：
num name sex age score addr
101 Ray Male 24 87.5 Beijing Road
102 Simon Female 28 99 Shanghai Road.China
103 Mason Male 25 100 Zhangjiang.Road
每个字段的分割符是Tab(也就是'\t')。现在程序要求可以随机访问表中的字段。经分析，表中的列数可以是固定的，用数组就可以表示出来，想具体访问哪个字段，直接array[field]即可。然后表格的行数就是文件的行数，这样以来表格就可以看成一个二维数组。但是每个字段是一个字符串，并且每个字符串的大小不能确定。
所以正好用一个三级指针来表示整张表格。由于行数，列数和字段长度不确定，这里动态分配内存。
程序很简单，关键的地方有两点：
1。三级指针的内存分配和释放。
第一步分配三级指针的内存，为表格所有行分配空间。 即
ptable->ptable_info = (char***)malloc(ptable->table_row * sizeof(char**));
让三级指针ptable->ptable_info指向row个连续地址二级指针的起始地址。
第二步分配二级指针的地址，为表格一行中所有列分配空间。即
*(ptable->ptable_info) = (char**)malloc(MAX_FIELD * sizeof(char*));
让二级指针*(ptable->ptable_info)指向colum个连续地址一级指针的起始地址。
第三步分配一级指针的地址，为表格一行中某列分配空间。即
*one_trace = (char*) malloc((strlen(one_line)+1) * sizeof(char));
让一级指针*one_trace指向字段字符串的地址。
释放内存空间则是相反的过程，类似c++中基类和派生类，构造函数和析构函数的调用顺序。
可以用valgrind来检查程序是否有内存泄露。关于valgrind，在Fedora下，yum install valgrind即可安装。
具体造作以后有时间再介绍吧。
2。分析表格中的一行。
实际上就是分割字符串。用到c标准库函数strchr.
#include
char *strchr( const char *str, int ch );
The function strchr() returns a pointer to the first occurence of
ch in
str, or
NULL if
ch is not found.
还有一个更简单的函数strtok
#include
char *strtok( char *str1, const char *str2 );
The strtok() function returns a pointer to the next "token" in str1, where str2
contains the delimiters that determine the token. strtok() returns NULL if no
token is found. In order to convert a string to tokens, the first call
to strtok() should have str1 point to the string to be tokenized. All calls after
this should have str1 be NULL.
For example:
char str[] = "now # is the time for all # good men to come to the # aid of their country";
char delims[] = "#";
char *result = NULL;
result = strtok( str, delims );
while( result != NULL ) {
printf( "result is \"%s\"\n", result );
result = strtok( NULL, delims );
}
The above code will display the following output:
result is "now "
result is " is the time for all "
result is " good men to come to the "
result is " aid of their country"
附上程序。
/*
* Print all the table info based on a table file.
*
* Usage : parse_table table_filename
*
* Author : Ray Chen
* Date : 2008-5-7
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define true 1
#define false 0
/*The max characters of a line*/
#define MAX_LINE_NUMBER 200
#ifndef NULL
#define NULL 0
#endif
//#define DEBUG
enum table_field{
NUM = 0,
NAME,
SEX,
AGE,
SCORE,
ADDR,
MAX_FIELD = 6
};
typedef struct table_info_type {
char*** ptable_info;
int table_row;
int table_col;
}table_info;
table_info my_table;
void usage(void)
{
printf("Usage : parse_table table_filename\n");
exit(true);
}
/*
* Return the line number of a file.
*/
int cal_file_lines(FILE *fp)
{
char line[MAX_LINE_NUMBER];
int count;
if(!fp) return -1;
rewind(fp);
count = 0;
while(!feof(fp))
{
fgets(line, MAX_LINE_NUMBER, fp);
++count;
}
return count-1;
}
/* Function: Parse one row of table, and save to pointers to pointers
* Input: string
* Output: pointers to pointers
*/
int parse_table_row(char* one_line, char** one_trace)
{
int switch_tag[MAX_FIELD];
char *result, *temp_line;
char** temp_trace;
int field = 0;
int loop;
result = temp_line = NULL;
temp_trace = one_trace; // backup
temp_line = one_line;
#ifdef DEBUG
printf("begin to parse one line\n");
#endif
if(!one_line) return -1;
if(!one_trace) {printf("one_trace is NULL\n"); return -1;}
for(loop = 0; loop < MAX_FIELD; loop++)
switch_tag[loop] =-1;
/* Split string taking '\t' as delimiters*/
result = strchr(one_line, '\t');
while(NULL != result)
{
*result = '\0'; // Now '\0' is delimiter
/* Record the position where the delimiters is changed */
switch_tag[field] = result - temp_line;
*one_trace = (char*) malloc((strlen(one_line)+1) * sizeof(char));
if(!*one_trace) {printf("Macalloc memory failed\n"); return -1;}
strcpy(*one_trace, one_line);
one_trace++, field++;
one_line = result + 1;
result = strchr(one_line, '\t');
}
/*Don't foret last field*/
*one_trace = (char*) malloc((strlen(one_line)+1) * sizeof(char));
strcpy(*one_trace, one_line);
/*Now temp_line is pointer to the last field. Recovery one_line,
* so that free the memory. Otherwise, memory leak!*/
one_line = temp_line;
one_trace = temp_trace;
for(field = 0; field < MAX_FIELD; field++)
if(switch_tag[field] != -1)
one_line[switch_tag[field]] = '\t';
#ifdef DEBUG
for(field = 0; field < MAX_FIELD; field++)
{
printf("%s\t", one_trace[field]);
}
printf("\n");
#endif
result = temp_line = NULL;
temp_trace = NULL;
return true;
}
/* Function: According to input file which contains trace table, save table info to a pointer
* to pointer to pointer.
* Input: file handler
* Output: table_info
*/
int setup_table_info(FILE *fp, table_info *ptable)
{
int row, result, len;
char*** temp_table;
char line[MAX_LINE_NUMBER];
if(!fp) return -1;
ptable->table_row = cal_file_lines(fp);
ptable->table_col = MAX_FIELD;
if(ptable->table_row == 0)
{
ptable->ptable_info = NULL;
return true;
}
/*malloc enough memory for table rows.*/
ptable->ptable_info = (char***)malloc(ptable->table_row * sizeof(char**));
temp_table = ptable->ptable_info;
if(!ptable->ptable_info) return -1;
rewind(fp);
for(row = 0; row < ptable->table_row; row++)
{
fgets(line, MAX_LINE_NUMBER, fp);
/*Skip the new line characters "\n"*/
len = strlen(line);
line[len-1] = '\0';
/*malloc memory for table coloum.*/
*(ptable->ptable_info) = (char**)malloc(MAX_FIELD * sizeof(char*));
if(*(ptable->ptable_info) == NULL) return -1;
result = parse_table_row(line, *(ptable->ptable_info));
if (result == -1) return -1;
(ptable->ptable_info)++;
}
ptable->ptable_info = temp_table;
temp_table = NULL;
return true;
}
/*
* Free memory.
*/
int cleanup_table_info(table_info *ptable)
{
int i,j;
if (ptable->ptable_info == NULL) return true;
for(i = 0; i < ptable->table_row; i++)
{
for(j = 0; j < ptable->table_col; j++)
if(((ptable->ptable_info)[i][j]) != NULL)
free(((ptable->ptable_info)[i][j]));
if (((ptable->ptable_info)[i]) != NULL)
free((ptable->ptable_info)[i]);
}
if(ptable->ptable_info != NULL)
free(ptable->ptable_info);
return true;
}
/*
* Print table.
*
*/
int print_table(table_info table)
{
int i,j;
if (table.ptable_info == NULL) return -1;
for(i = 0; i < table.table_row; i++)
{
for(j = 0; j < table.table_col; j++)
printf("%s\t", (table.ptable_info)[i][j]);
printf("\n");
}
return true;
}
int main(int argc, char** argv)
{
char *filename;
FILE *file;
int result;
/* The argc must be two! */
if (argc != 2) usage();
/* Setup environment */
filename = argv[1];
if (filename == NULL)
{
printf("File name can't be null\n");
usage();
}
/* Check file */
if ((file = fopen(filename, "r")) == NULL)
{
printf("%s doesn't exist\n", filename);
usage();
} else {
printf("Begin to parse %s\n", filename);
}
/* setup table info */
result = setup_table_info(file, &my_table);
if (result == -1) {printf("setup_database failed\n");exit(1);}
result = print_table(my_table);
if (result == -1) {printf("trace table is blank!\n");exit(1);}
/*Cleanup */
cleanup_table_info(&my_table);
fclose(file);
return true;
}
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