C语言读取CSV文件的方法2

在之前的文章中，我们已经介绍了利用strok()函数对CSV文件进行解析的基本方法。本文将在此基础上更进一步，我们要将一个用CSV文件存储的表格数据放进一个二维数组中。首先来看看作为示例的一个小型的CSV文件内容：

我们特别约定，CSV文件的第一行的第一个数字表示正式的数据文件一共包含的行数，第二个数字则表示数据文件所包含的列数，注意这里的行数和列数是不包括第一行本身的。

下面我们给出了读取该CSV文件的示例程序：

#include <stdio.h>#include <string.h>#include <stdlib.h>int main(int argc, const char * argv[]) {        char file_name[] = "test_data.csv";    FILE *fp;    fp = fopen(file_name, "r");        if (!fp) {        fprintf(stderr, "failed to open file for reading\n");        return 1;    }            int idx = 0;    size_t len = 0;    char * line = NULL;    char * element;        getline(&line, &len, fp);    size_t lines_size = atoi(strtok(line, ","));    size_t items_size = atoi(strtok(NULL, ","));        double **array;    array = malloc(lines_size * sizeof(double*));    if(NULL == array){        fprintf(stderr, "failed to allocate memory\n");        return 1;    }    while ((getline (&line, &len, fp)) != -1) {                array[idx] = (double*) malloc (sizeof(double) * items_size);        element = strtok(line, ",");        for(int j=0; j<items_size; j++){            array[idx][j] = atof(element);            element = strtok(NULL, ",");        }        idx++;    }        fclose (fp);        //Test code    int row = 0;    for (; row<lines_size; row++) {        printf ("array[%d][] =", row);                for (int col=0; col<items_size; col++)            printf (" %f", array[row][col]);                printf("\n");    }        //free every line    for (row = 0; row < lines_size; row++)    {        free(*(array + row));        array[row] = NULL;    }        free(array);    array = NULL;    return 0;}

上述代码中特别值得关注的地方有两个：1）二维数组的动态创建和释放；2）我们在读取文件是用到了getline()函数。这是早期版本的C语言中并没包含的一个函数（彼时我们一般用fgets()来代替）。The latest and most trendy function for reading a string of text is getline(). It’s a new C library function, having appeared around 2010 or so. 该函数的原型如下：

getline(&buffer,&size,stdin);

各个参数的意思为：

• &buffer is the address of the first character position where the input string will be stored. It’s not the base address of the buffer, but of the first character in the buffer. This pointer type (a pointer-pointer or the ** thing) causes massive confusion.

• &size is the address of the variable that holds the size of the input buffer, another pointer. 

• stdin is the input file handle. So you could use getline() to read a line of text from a file, but when stdin is specified, standard input is read.

最后执行上述程序，其输出结果如下：

array[0][] = 85.000000 67.000000 34.000000array[1][] = 27.000000 82.000000 100.000000array[2][] = 1.000000 23.000000 98.000000array[3][] = 35.000000 62.000000 78.000000array[4][] = 21.000000 45.000000 66.000000

（全文完）