在文件中找到字符串后替换它旁边的字符

Question

My code is to accept the values from the command line args and search for string and replace the next character after the string found in the line where the keyword in each line is separated by separots.

Basically after finding the character position from the buffer string which corresponds to file pointer position of that string, then update the character at fp+X. I want to know is there a way to do it?

I am ok with C++ too.

I have the file.txt like below

FOO,val1=0,val2=0
BAR,val1=0,val2=0
TOO,val1=0,val2=0

Command line

#./a.out FOO val1 1

mycode.c

char        buffer[kKEYWORD_SIZE];
FILE*       fd;

if ((fd = fopen(file.txt, "r+")) != NULL)
{
    do
    {
        memset(buffer, 0x0, kKEYWORD_SIZE);
        if (fgets(buffer, kKEYWORD_SIZE, fd) != NULL)
        {
           //storing the entire line into pointer to character array.
            for (index = 0, token = strtok_r(buffer, sep, &last); token; token = strtok_r(NULL, sep, &last), index++)
                strcpy(*(keyword + index), token);


           // the first keyword found and search for 2nd keyword and replaces its value   
            if (strcmp(*(keyword + 0), key1) == 0)
            {
               if ( ( find = strstr(buffer, key2 )) != NULL )
                {
                      // I want fp pointers to move it to find+5
                      fputs(fp,argv[3]);
                }

it would be greatly appreciated if any one throw a light on this

Answer 1

Well it is not very clear to me, what are you trying there, but If this is not what you need, please let me know:

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

int findFOO( const char *const ptr, const char *const substr );
int search( const char *const src, const char *str );

size_t findOCC ( char *const src, const char *substr );

int main ( void )
{
    char arr[] = "FOO,val1=0,val2=0" ;

    printf("Before: %s\n", arr );

    size_t len = findOCC( arr, "var1" );
    arr[len] = '1';

    printf("After:  %s\n " , arr );

}

int findFOO( const char *const ptr, const char *const substr )
{
    char *ret = strstr( ptr, substr );
    if ( ret == NULL )
    {
        return 0;
    }
    return 1;
}


int search( const char *const src, const char *const str )
{
    int i, j, firstOcc;
    i = 0, j = 0;

    while (src[i] != '\0')
    {

        while (src[i] != str[0] && src[i] != '\0')
            i++;

        if (src[i] == '\0')
            return (-1);

        firstOcc = i;

        while (src[i] == str[j] && src[i] != '\0' && str[j] != '\0')
        {
            i++;
            j++;
        }

        if (str[j] == '\0')
            return ( firstOcc );
        if (src[i] == '\0')
            return (-1);

        i = firstOcc + 1;
        j = 0;
    }
    return 0;
}

size_t findOCC ( char *const src, const char *substr )
{
    char buffer[strlen( src) + 1 ];
    strcpy( buffer, src );
    if ( findFOO ( src, "FOO" ) )   /// Search if there is a Line containing FOO
    {

        int ret = search( buffer, substr );
        if ( ret ) /// found a Match
        {
            char *tmp = strtok( buffer, "=" );
            return strlen( tmp ) + 1; /// return the index
        }

    }
    return 0;
}

Output:

Before: FOO,val1=0,val2=0
After:  FOO,val1=1,val2=0

I was not searching in a file, because you need a way to modify your buffer, so I will let you to do the rest of the Job here.

Of course there are a lot of error checking needed here, but I am sure that you can figure out what you need to do.